Only Children and Cognitive Ability in Childhood: A Cross‐Cohort Analysis over 50 Years in the United Kingdom

Only children's uniqueness has intrigued researchers for decades, but many gaps in knowledge remain as to whether only children differ from children who have siblings. We use data from four British birth cohorts (born in 1946, 1958, 1970, 2000–2002) to investigate cross‐cohort differences in the composition of only child families and whether the association between being an only child and cognitive ability in childhood has changed over time. Only children show similar scores to children from two child families and higher scores than children with two or more siblings across each of the cohorts analyzed. However, the results also show that—consistent with the finding that, across cohorts, the composition of the only child group has become more associated with social disadvantage—the “only child advantage” has weakened when comparing the most recent birth cohort to the older ones. Adjustment by family sociodemographic characteristics attenuates within and cross‐cohort differences. Moreover, the results show that the cognitive advantages associated with being an only child vary considerably by whether the cohort member has been exposed to parental separation or is growing up in a family with lower socioeconomic status. The results highlight diversity in being an only child whose characteristics are conditional on changes throughout time and society.