Speaking of recycling, (thanks, Cheri) this is SUCH a fun activity that I loved a as a kid, and just as much as a Mom.
Collect large boxes (I mean, HUGE, if you can). Or call your local supply store (Sears, Menards, Home Depot, etc.) and arrange to pick up some boxes before they crush them. Know someone who just moved in? Or a neighbor or friend who is getting a new appliance? Chances are good they have boxes that you can use.
Refrigerator boxes are the best -- a veritable sky scraper for anyone under 3 and a half feet tall! All you need are some markers or paints, a craft knife, and maybe some strong clear packing tape. A dash of imagination (or click on the links) and you've got yourself a new play house or mode of transportation!
With a little pre-planning, you can construct elaborate castles, pirate ships, or a maze. For the more ambitious, Mr. McGroovy’s website has plans for all these, as well as instructions for cardboard trains, a princess carriage, fire trucks and more. (The website also sells special rivets that make connecting cardboard boxes a snap — literally.)
But if you're a Mom like me, I'm looking for quick and easy ideas to fill an afternoon. That's when I remember decorating the box with markers, then just having fun getting in with my friends, or rolling it down the yard.
Or cut it out to lay flat and you have a giant canvas for finger paints (foot paints, even), or the biggest city you can draw for these guys to play cars on.
It's been over 25 years, and these memories are still going strong for me. I hope for the same for you and your kids!