The boys were given a foam rocket to play with in the garden: it works when you push a tube into another tube and fires the rocket out uing air pressure.  No batteries or silly noises.

Youngest Son is seen making a test shot across the valley. Note rocket at extreme right.

It worked well until he realised that bracing the tube against the ground meant you could fire the rocket much higher. It now resides near the top of a holly tree and will remain there until it finally falls down again.