A.C.
My 3.5 yr old LOVES his puppy tent. He plays in it all the time and my 14 mo old will crawl in there with him and they will giggle for 15-20 minutes.
Here's something kind of like it:
http://www.amazon.com/Elephant-Animal-Tunnel-Children-Pla...
Oh, and the tent folds up really fast, making clean up a breeze.