I agree with the others - if he's good in other areas then I wouldn't worry too much. My DS is 3.4 yrs and only recently starting including the number 7 lol! For some reason he would always leave it out and then one day it just 'clicked' and now he gets it right every time. Also it might just be one of those things that he isn't interested in right now as obviously he is so good at other things that his little brain is so busy that it just cant' fit in counting as well lol! I would just keep making it fun!