Do you get lots of junk mail? Turn junk mail into free educational materials and boredom busters for your younger writers. Gather up the little business reply cards that you have to fill out with your name, address, etc. if you are going to order something. Save them so that if your child gets fidgety during a trip, or in waiting rooms, etc. you can hand one to him or her to fill out. The child will practice filling in her own name, address, telephone number, and other pertinent information. This helps with writing practice, and memorization of important safety information such as your address and telephone number. Just make sure that the cards don't make it to the mailbox without your consent!
Give your slightly older child a catalog that has a pull-out order form. Tell her how much "money" she has to spend, and that she must order as much as she can from the catalog without going over. Point out that some of her budget has to go to shipping and taxes. You can decide if you want her to be able to use a calculator for this lesson, or not.
Also try using catalogs for Challenge #2!