"you're not the boss of me," a plaint often heard on the playground, is best related to the concept of

This is very much related to the concept of authority, or lack of, in this particular situation. If a child would say "you're not the boss of me" to another kid, he or she does not recognize that kid as an authority figure and expresses defiance if the kid tells him or her to do something. 

I believe the answer you're looking for is "object permanence".