Sometimes, even 3-year-olds just want to fit in with the group. What makes preschoolers eat their veggies? Raise their hand? Wait their turn? 'Because I say so' is a common refrain for many parents. But when it comes to getting kids to behave, recent research suggests that the voice of adult authority isn't the only thing that matters. Around age three, fitting in with the group starts to count big too. Source 4j.