Children often want certain items at the grocery store (ok make that usually/always). If treats are in the family budget, younger children can be given a number of items that they can pick (one is absolutely fine and appropriate). If a package of treats is purchased, they can be counted, and agreed to be consumed one day at a time, or shared with family members (again counted to make sure there are enough). Older children can be given a monetary amount that they can spend. And even with young children it is never too early to explain what a budget is, and what can and can not be included in the family budget – another authentic way to reinforce math concepts.