Active mediation, restrictive mediation, and media co-use are widely discussed strategies of parental mediation. This chapter reviews their theoretical framework in the context of social media activities. It suggests media trusteeship as a complementary approach to parental mediation that parents especially apply until their new-borns, infants, and toddlers have developed abilities to use digital media autonomously. The transitional process from trusteeship to parental mediation is further investigated empirically based on 29 in-depth interviews. The results indicate that although parents believe digital media will be a vital part of their children’s lives, most parents are unaware of their trusteeship and its fluidity. Parents possess only limited concepts of how they could support their children’s digital media development. Instead, they seem to be driven by the transformations of social media and apply ad-hoc tactics to cope with changes of their children’s media autonomy