I think it's only entrapment in a legal sense if the cop tells you take the sneakers. Simply presenting someone an opportunity to commit a crime isn't entrapment.

If a cop went over to the kids and said "hey look, that truck is full of sneakers and no one is around, so you should go take them" that would be entrapment. But the sneakers just being there and the kids on their own accord deciding they should steal them isn't entrapment.

It's a really shitty thing to do to be sure, but doesn't fit the legal definition of entrapment as far as I know.