If you want my advice, keep somewhere an old mouse and an old keyboard with no battery & no wires for the days where he will want to imitate you.(soon half a year max) He'll be happy to have those and you will have your good keyboard in one piece :D
My monsters did start to play around 3,5yo to minecraft in creative mode, close to the wooden block, easy to understand, no monster, no stress a perfect game to start :)