Objective: To understand the current situation of the social development between only children and firstborn of young age, so as to provide a reference for the promotion of the social development of young children. Methods: Stratified cluster sampling method was used to select 734 only children and firstborn children aged 3-9 in two kindergartens and two primary schools from grade 1 to grade 3 for questionnaire survey in Bengbu City. The content included the general information of children and their parents and the social assessment of children. Results: The rate of emotional symptoms in firstborn children(27.8%) was higher than those of only children (17.6%)( χ 2=9.45, P <0.01). The results of univariate analysis showed that the rate of hyperactivity and inattention in social development of both only children and firstborns decreased with the increase of family socioeconomic status ( P < 0.05 ). Multivariate Logistic regression analysis of only children showed that only children with high economic status had a lower risk of hyperactivity and inattention and had a higher risk of peer interaction( P <0.05). The prosocial behavior of girls was better than that of boys in the aspect of social development of only children and firstborn children( OR =1.70, 2.85, P <0.05). For only children, the occurrence risk of being difficult was lower when the primary caregiver was parents than grandparents( OR =1.63, P < 0.05 ). For firstborn children, the risk of being difficult in nuclear families was lower than that in third generation families( OR = 2.14 , P <0.05). Multivariate analysis of the only child showed that boys had higher risk of hyperactive attention and less prosocial behavior than girls ( OR =2.24, 1.70, P <0.05), and a lower risk of developing mood disorders than girls( OR =0.57, P <0.05). The social development of only children varied among different grades, and the risk of abnormal prosocial behavior was lower with the increase of grades ( P <0.05). Conclusion Higer family social status is positively associated with children s social development level. But parents with high economic status should also avoid too much material and spiritual doting. Parents should strengthen their own learning to enhance the level of socialized education, raising siblings equally, improve the quality of parent child relationship, and promote the all round development of children s socialization level.