My sister bought my eldest son this pop up bus when he was two and it has been a hit with him and all my other kids.  this bus is made a simple nylon and can easily be folded into a small circle that can fit in a cupboard, drawer, closet, car trunk, etc.  However, once unfolded (which takes literally like 5 seconds) it is a huge bus that quite a few kids can fit in at once and adults too!  It has two doors so the kids can get in and out easily and because it is just nylon it doesn't them or anything else if it falls over.  On the down side though, because it is so light weight if you are playing...