Preschool children are at the initial stage of individual development and at a critical period in cultivating their approaches to learning. In the context of China’s frequently adjusted birth policies, further research is necessary on children’s approaches to learning in families of different sizes. A questionnaire survey was administered to 5454 only child and 4632 non-only child parents from the east, middle, and west of China. The study found that children’s approaches to learning generally developed well, but non-only children’s approaches to learning was significantly lower than those of only children. There are four profiles of approaches to learning for both the only children and the non-only children. This study also found that gender, social skills, family income, and type of preschool exert significant influences on children’s approaches to learning. Parents’ educational background had a significant influence on only children’s approaches to learning but had no significant influence on non-only children’s approaches to learning. We provide practical implications for promoting children’s approaches to learning in families of different sizes.