Has anyone else allowed a child to play in the drivers seat of a recently restored car?

Of course you should. If you don't, every time you look at that car you will be reminded of your lack of generosity. But take precautions. Kids are kids. Make sure his hands are clean, make sure he knows he has to be careful with it. Put the top down and drive him around the block. I spent many happy years driving a Spitfire....enjoy it and enjoy sharing it.