Despite having strong bonds with their parents, only children often regret having grown up without siblings. In 2001 Lisen Roberts of Western Carolina University and Priscilla Blanton of the University of Tennessee Knoxville asked young adults to look back on their childhoods. Many found it particularly unfortunate they did not have a trusted playmate as those with siblings had. In fact, preschool-aged only children often developed imaginary friends with whom they could be allies and share everyday things. But there’s no reason for concern—creative play with imaginary companions promotes social development and the ability to communicate.

There are, however, indications only children are less willing to come to terms with others. In new findings from China, where the one-child policy dictated family planning for nearly four decades, researchers led by psychologist Jiang Qiu of Southwest University, Chongqing, examined 126 students without siblings and 177 with siblings in terms of thinking ability and personality. In one survey only children achieved lower scores in terms of how tolerant they were. According to the five-factor model (FFM), a model of personality dimensions, particularly tolerant people are altruistic, helpful, compassionate and cooperative. Intolerant individuals are often characterized as quarrelsome, distrustful, egocentric and more competitive.