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Those long-standing stereotypes have deep roots in psychology. G. Stanley Hall, PhD, the first president of APA, wrote that being an only child is “a disease in and of itself.”

But the American family is changing. The share of mothers who had one child doubled between 1976 and 2021, when it reached 22%, according to Pew Research Center data. The U.S. birth rate is at an all-time low, and nearly half of childless adults say they are unlikely to have children, citing financial concerns, climate change, and lack of supportive policies for parents.

[Related: Americans are having fewer kids—if they have them at all]

“Women are also waiting longer to start their families, so many are hitting a fertility wall. That’s a big factor in this huge swing toward the one-child family,” said Susan Newman, PhD, a social psychologist who has written extensively about parenting.

The trend toward smaller families extends abroad, too. Of households with children in European Union countries, 49% have one child; South Korea, Japan, Italy, Spain, Canada, and China are among the countries with fertility rates lower than that of the United States (Fertility Rate, Our World in Data, 2024). Though birth rates in most African countries are much higher, they are also rapidly declining (A dramatic drop in fertility across Africa, Agence Française de Développement, March 5, 2021).

Given that one-child families are on the rise in many countries, what is known about how only children fare? Do the stereotypes hold true? Though research on the subject is limited, evidence suggests that overall, people who grow up with and without siblings do equally well. Only children may face some unique challenges such as high parental expectations and special advantages such as more attention at home, but they do not show substantial differences in personality, cognition, social aptitude, or well-being.

Only children did at least as well as other kids on cognitive tests during childhood and measures of well-being in adulthood, according to research that compared four cohorts of children born in the United Kingdom in 1946, 1958, 1970, and between 2000 and 2002 (Goisis, A., et al., Population and Development Review, Vol. 49, No. 2, 2023; Chanfreau, J., & Goisis, A., Ageing & Society, Vol. 44, No. 1, 2024).

“Are only children really spoiled, lonely, bossy, and aggressive, with more imaginary friends?” asked Newman, who authored the book Parenting an Only Child: The Joys and Challenges of Raising Your One and Only. “That stereotype is so far from true, but when you get a cultural thinking that’s buried so deep, it can be very hard to change it.”

Though the birth rate continues to decline, most Americans still think the ideal family has more than one child. In a series of Gallup polls conducted in 2023, 44% of U.S. adults said having two children is best and 45% said having three or more children is ideal (Brenan, M., Gallup, September 25, 2023).

“Many people still believe that it’s a moral obligation to have children—and that is plural. One is not enough,” Falbo said.

Early psychology research, dating back to 1896, played a part in reinforcing those beliefs. Hall said children without siblings tended to be “jealous, selfish, egotistical, dependent, aggressive, domineering, or quarrelsome” because of the undue attention they demanded or received. His conclusions rested largely on observations from the disproportionate number of only children he saw in his clinic and an anecdotal research effort he oversaw, “A Study of Peculiar and Exceptional Children” (Bohannon, E. W., The Pedagogical Seminary, Vol. 4, No. 1, 1896).

“Hall concluded that only children were particularly at risk. But the other option is that parents of only children had the time and resources to take their child to a guidance center,” Falbo said.

That pattern is precisely what Carl Pickhardt, PhD, a counseling psychologist and parenting expert, observed during 30 years of private practice in Austin, Texas. He has worked with a large share of only children—not because kids without siblings were more troubled or maladjusted, but because their parents were highly vigilant, he said.

“All of their focus was on this kid, and if they saw something they couldn’t understand or had trouble dealing with, they sought help to try to comprehend it,” said Pickhardt, who authored the book The Future of Your Only Child: How to Guide Your Child to a Happy and Successful Life.

Many parents who have a single child invest the entirety of their resources—time, money, and energy—in that child’s future, as well as their emotional needs and parental expectations. That focused attention can come with both benefits and challenges. The research is mixed, but only children appear to perform at least as well academically as children who grow up with siblings (Downey, D. B., American Psychologist, Vol. 56, No. 6–7, 2001).

“They get the precious gift of full attention from their parents without distraction, which is beneficial for their cognitive development, in particular linguistic development,” said Linda Blair, PhD, MPhil, a clinical psychologist based in Bath, England, and author of the book Birth Order.

The unrivaled attention of parents can be empowering, but it can also be overwhelming. Only children are acutely aware that theirs is the only report card coming home, Newman said. Bearing the full burden of parents’ expectations and emotions can also make it harder for only children to develop and embrace a separate self—particularly during adolescence—a period key for differentiation, Pickhardt said.

“There’s no free lunch in this world,” he said. “There are costs and benefits to being only; there are costs and benefits to having siblings.”

Large-scale research studies have searched for personality differences between only children and those with siblings, but most have found only minimal effects, if any.

“For a long time, people have stereotyped only children as being selfish and egotistical. They’ve absorbed all of Mom and Dad’s love, and they’re unable to share and cooperate with others,” said Joshua Foster, PhD, a professor of psychology at the University of South Alabama. “All of these negative stereotypes can roughly be thought of as narcissism.”

Foster and his colleagues administered two measures of narcissism to 8,689 college students, finding no differences between people who grew up with versus without siblings. They also found no differences in specific facets of narcissism, such as arrogance or entitlement (Personality and Individual Differences, Vol. 161, 2020).

In another study of personality traits, psychologist Samantha Stronge, PhD, a researcher at the University of Auckland in New Zealand, investigated the Big Six personality traits (honesty-humility, emotionality, extraversion, agreeableness, conscientiousness, and openness to experience) in a sample of more than 20,000 New Zealand adults. Only children reported slightly lower levels of conscientiousness and honesty-humility and slightly higher levels of neuroticism (emotionality) and openness to experience, but all differences failed to reach the threshold for a small effect size (Journal of Research in Personality, Vol. 83, 2019).

“Beliefs about only children appear to contradict actual group differences,” the researchers concluded.

But there is no denying that for most kids, growing up without siblings is qualitatively different. The house is quieter, sibling rivalry is not a thing, and their closest confidants might be adults—factors that can, in theory, influence a child’s social development.

Adolescence can be an especially challenging time, as children who have borne the full weight of their parents’ expectations and approval enter a phase of life where individuation is key. For an only child, that differentiation and opposition require extra courage, Pickhardt said.

“These are hard things to do, particularly if you’re an only child,” he said. “You don’t want to alienate your parents—they’re the most important people in your world.”

Older research suggests that overall, only children tend to have more positive relationships with their parents than children with siblings (Falbo, T., & Polit, D. F., Psychological Bulletin, Vol. 100, No. 2, 1986). Skills developed in those relationships often translate into healthy interactions with adults outside the family, too, Pickhardt said.

“Only children learn early on how to get along with adults, which is a huge advantage,” he said. “When they exit adolescence, their emotional sensitivity and social skills for getting along in the adult world are typically very well developed.”

Do better social skills in the adult world come at the cost of peer relationships? One longitudinal study suggests only children may be less social at school. Researchers from Project Talent, a large longitudinal study of U.S. youth that tracked well-being and life outcomes, interviewed more than 400,000 teenagers in 1960 and several times thereafter, finding that only children were more interested in solitude than their counterparts with siblings (Flanagan, J. C., et al.,The Project TALENT Data Bank: A Handbook, 1972).

Those differences may not cause long-term harm. Though no large-scale studies have examined sibling effects on loneliness throughout the life span, some data suggest that only children are not lonelier later in life (Lin, S., et al., American Journal of Orthopsychiatry, Vol. 91, No. 4, 2021).

“The greatest gift of being an only child is that you learn to be content with your own company and spend a lot of time with yourself. And that’s huge,” Pickhardt said. “After all, our primary relationship in life is with ourselves.”

With more alone time, only children may also have extra opportunities to explore their creativity and learn time management skills from an early age, Newman said. A study of 303 young adults in China found that only children scored higher than people with siblings on cognitive flexibility (a measure of creative thinking) and that those higher scores were related to differences in brain structure (Yang, J., et al., Brain Imaging and Behavior, Vol. 11, 2017).

The study also found that only children were less agreeable than people who grew up with siblings. Another Chinese research group measured the neural signatures of trust by conducting simultaneous brain scans of participants playing a game together (a technique known as hyperscanning) and found that only children showed less interpersonal synchronization in the medial prefrontal cortex than people who grew up with siblings (Wu, S., et al., Brain and Cognition, Vol. 149, 2021).

In clinical work, Pickhardt observed a related pattern. Only children often struggled with conflict and joint decision-making, issues that arose during their early romantic relationships and required special attention. He suggested that the lack of exposure to the rough and tumble of sibling rivalry and play could be one cause of discomfort with conflict.

A struggle with shared decision-making could impact some people’s long-term relationships. A study using data on more than 57,000 people, collected by the University of Chicago’s National Opinion Research Center between 1972 and 2012, found that only children were slightly more likely to get divorced than people with siblings. Each additional sibling was associated with a 3% drop in the chance of divorce (Merry, J. J., et al., Journal of Family Issues, Vol. 41, No. 2, 2020).

As children, people without siblings may benefit from receiving all the family’s resources, but that advantage may disappear—or even become a burden—later in life. In the study of only child cohorts in the United Kingdom, demographer Alice Goisis, PhD, found that only children were more likely to provide care to their aging parents in middle adulthood (Ageing & Society, Vol. 44, No. 1, 2024). That can include the combined responsibilities of power of attorney, tax preparer, physical caretaker, and more.

“What in earlier life was a resource can potentially become a disadvantage later in life,” said Goisis, an associate professor of demography and research director in the Centre for Longitudinal Studies at University College London.

Goisis’s research also helps challenge the stereotypes of growing up without siblings. By comparing the only child experience across different countries and time periods, she and others have shown that differences in outcomes are better explained by parental resources than a universal “only-child syndrome.”

“It’s not so much being an only child per se, but what does being an only child mean in different times and places?” she said.

In the United Kingdom, only children landed in the middle of the pack on socioeconomic measures such as parental education and income and did at least as well as children with siblings on cognitive measures and when it came to overall well-being (Population and Development Review, Vol. 49, No. 2, 2023).

In other countries, being an only child looks different. A long-standing two-child norm in Sweden meant that for many years, families with a single child had fewer resources. Research shows that only children in Sweden have worse long-term health outcomes than people from larger families: They are more likely to be overweight or obese in adolescence and more likely to die before age 50 (Keenan, K., et al., Population Studies, Vol. 77, 2023).

Only children born under China’s one-child policy, by comparison, appear to have better mental and physical health than their counterparts with siblings. Many only children were raised by educated urban parents who—if allowed by law—could have afforded to support a larger family (Falbo, T., & Hooper, S. Y., American Journal of Orthopsychiatry, Vol. 85, No. 3, 2015; Short, S. E., et al., in Kaufmann, E. P., & Wilcox, W. B., [Eds.] Whither the Child? Causes and Consequences of Low Fertility, Routledge, 2013).

“We should avoid overgeneralizing to anyone who’s an only child, because within that category there will be a multitude of experiences,” Goisis said.

The paucity of research on only children makes it hard to draw clear conclusions about the prospects for those who grow up without siblings. Virtually all findings are correlational, said Blair, and it can be hard to know what other variables to control for when making comparisons.

Foster suggested that the lack of publications could, in part, be driven by research like his narcissism study, which found no effect. “We’re getting better at publishing null effects than in the past, but there’s still a bias against them,” he said.

More insights on how only children do across contexts, as well as later in life, could help paint a clearer picture of what it truly means to grow up without siblings.

“There has been a lot of focus on the early child period, but extending the focus to other stages of life, showing that these children develop well into adulthood, will also help debunk the stereotypes,” Goisis said.

As life trajectories and family priorities continue to shift, only children may soon outnumber children with siblings in many countries. Contrary to the stereotypes, those conducting research say that is not a cause for concern.

“It’s a necessary trend that we are having fewer children,” Blair said. “With every birth order position, there are great assets and there are drawbacks. But this is undoubtedly a very positive way to grow up.”