There is a sharing policy at my son's preschool. It's a parent-run co-op, so we have to have policies like this so that we will all handle situations relatively the same way. The policy is that a child can keep a toy as long as they want to. If another child wants the toy, they have to wait until the first child is done with it. We'll even "save" toys for the child if they have to go to the bathroom, go to the snack table, etc. so that it won't get taken before they're done. This applies to anything in the yard or school that can be played with, including swings and monkey bars.