Have a garage sale. This can have several benefits. One, you'll clean out the closets, garage and attic. Two, you'll make money. They can practice their math skills by adding up purchases and making change.
Little ones can make lemonade for customers.
Take a trip on the Internet. If a far-away family vacation is just too expensive, try taking a day trip on the Internet. Let everyone choose a country, and then find everything you can about that country. Each family member can create a traditional costume for that country, and perhaps the evening meal could be a smorgasbord of delights from all the cultures you've discovered. If you don't have a home computer, the library has computers available to the public.