Trying to come up with a series of simple science labs/experiments to do w/ my science infatuated 4 year old.

I want to stay away from bunsen burners and other hazards and any complex apparatus (I want my DS to be a participant, not a spectator). I can think of a few (maybe static and dynamic friction by pulling blocks off a table etc), making (and sinking) boats out of foil etc. Any ideas are welcome.