If t hey are still paying you for the full time space even though the child is at preschool then you could provide the snack if you wanted to but certainly not if the parent is not payingn for the equivalent time in your daycare. At the same time when I took school age my contract did say "any food for outside the daycare was to be provided by the parent". I probably would say that snack at preschool is the parent's responsibility since they chose for the child to attend. It is not your job to make a separate snack for the child to take with them.