Although this is more a lifestyle than a one time family activity, it is imperative to teach our children, our families, about stewardship. Kids need to learn early about how to save, spend and give money. Giving them small amounts of money (whether allowance, pay for chores, or gifts) to practice with is a great tool to really imbed these concepts in their minds. They can start while still young giving to charities and making purchases for the things they want (gum, candy, etc.)
As they age it is important for families to impart the practice of saving money too. One day these same kids will want to make bigger purchases (shoes, movies, etc.) Having them learn to put off these purchases while saving money is crucial. This way once these kids enter early adulthood they will be well versed and ready to pay for entertainment, buy a car and even buy a house (whether using something like VA home loan rates or a cash downpayment.)
These type of family activities throughout family life will prove invaluable to parents, kids and society alike.