How about a castle/fort with lots of horses and knights? Someone is selling one on here but it might have gone. I've still got a great one which my son played with for ages and I get it out for the children I look after when they get to a certain age. If your son enjoys Thomas maybe buy a couple of Thomas magazines with the activities to try and there's always a freebie on the front which keeps them occupied for a while. If not try another magazine which his grandmother could look at with him. There's always stickers and free crayons on the magazines which encourage mark making/colouring in. You'll be surprised at what children enjoy with different people. If he likes Ninja turtles, I wouldn't worry too much. My son loved them too and Power Rangers and Action Man (still have the Action Man advert song in my mind) "Action Man the greatest hero of them all". He was a little bit older than your son if I remember but he's 22 now and doesn't remember much of it. Playing with water is always a hit, even if it's a bowl in the kitchen sink and washing up. Stickle bricks and lego are good too.