We bought these Air powered stomp rockets at a garage sale, but they can be bought online at http://www.iqkids.net/higperstomro.html for $9.99. The box says they are for ages 8 and up, but my grandson was 3 when we bought these last summer and he loved them.
They are very simple even for a three year old to use. You get a launching pad and 7 rockets with the set. The launching pad is just a plastic tube with a plastic base attached to a tube that then attaches to the plastic stomp pad. The rockets are slid onto the plastic tube and when my grandson jumps on the stomp pad the air pushes the rocket into the air. The box says the rocket will fly 400 ft., but my three year old grandson could only get it to go about 100 ft. I never tried it myself, but I believe it would probably go 400 ft. if you stepped on it hard enough.
The only negative about the product was that the plastic tubing got folded in the box and it was hard to get it to stay straightened out so the air could go through it easily. Other than that even though everything was made out of plastic it held up and we only lost a couple of rockets, which I found while mowing the lawn.
I would recommend this for any child, my grandson loved it!