id make them work for it do chores to "pay" you back for it they didnt work for it you did so they need to work to pay you back or do push ups, jumping jacks, sit ups or run laps.

for every piece of candy thats stolen take something from the child lol...see how the child likes it in return. or for every piece they have to do 10 push ups or something. just to make sure they dont do it again lol...