Make your kitchen into a grocery store and let the child be the checker. Make the food in the pantry certain prices that will allow the child to add, subtract or whatever you choose.
You can return things to the "store" and he/she can subtract the price from the total bill and give you a refund. Use or make play money.
Or you can use the items in your closet for a clothing store (more for a girl I think) and do the same things. It is great fun. The child is playing but learning.
Or if they have an ample bookshelf in their room, you can play bookstore or toy store with their toys - tons of possibility but all can be used to practice basic math skills.