A safety pilot may be a good idea, but if you have an airplane-mad kid, why not let him do some flying. It won't take a huge amount of informal instruction to enable somebody to fly somewhere (on the GPS moving map) and get the plane down. Obviously a 5 year old can't, but plenty of schools have been doing the informal "co-pilot" courses whose objective is just that. I am certain my 12 year old could do it, and walk away, and he's had only a few flight in the RH front seat.