My son did a part day pre k like program last year and they used computers for educational games. He starts pre K today and they will use computers too but he never asks to use ours at home. If he did, once in a while would be fine with my supervision but I wouldn't buy him is own lap top. Kids are too plugged in now days and I don't think the schools help with that either. My daughter just started 5th grade and I asked her teacher about spelling words since she hadn't brought any home and I was told no spelling words because there is spell check! WTH!! Just because there is spell check doesn't mean my child still doesn't need to learn how to spell is what I told her. And this nonchalant attitude towards electronics and children has got to stop otherwise if it isn't on the tv, nintendo, playstation, or computer kids aren't going to know how to learn by simply exploring their own world around them with their own two hands.
Just my 2 cents, but no, your son doesn't need a lap top or anything else of that nature unless it is a Lmax from Leapfrog.
Good luck
S.