A meta-analysis on the development of prosocial behavior by Eisenberg and Fabes (1998) found significant age differences in the sharing behavior, with older participants being more prosocial than younger children. Recent studies using simple economic games also found that children's altruistic behaviors increases with age (Benenson, et al., 2007; Blake & Rand, 2010; Fehr, et al., 2008; Harbaugh et al , 2003); However, Zhu et al. (2008) found that from 8 to 18 years old, Chinese children's offer decreased in Dictator and Ultimatum Games (DG and UG), though their offers were higher than their German counterparts in the cross-cultural study. To explore whether Chinese children show a culturally different development trajectory from their western counterparts, the current study investigated even younger children from 4-9 years olds on the development of their sharing behavior in DG and UG. The study also further explored the correlation between children's sharing behavior and their theory of mind. In study 1, four age groups of children were instructed to be playing with good friends from the same class (in-group members) or anonymous peers from different schools (out-group members) in DG as proposers, to explore the development of sharing behavior and whether there would be an in-group bias in their sharing behavior. In study 2, children were instructed to play as responders in four mini-ultimatum games (Mini-UG) while each game showed different intention of the proposer, their rejection behavior to unfair offers was investigated. Children's Theory of mind was measured by first and second order false belief tasks. Results showed that: 1. children's offer in DG and in-group bias increased with age. 2. School-age children rejected unequal allocation more often in UG than preschoolers, and they tended to consider the proposer's intention, while younger children less so. 3. Preschool children's sharing behavior and rejection to unfair offer was correlated to their theory of mind, but ToM played a less important role with school age children.