I agree with the others. DS loves the Marketplace but Pleasure Island is more for adults at night. Even though it's a "Disneyfied" night club area, there are still adults drinking and letting loose without the kids.
You may want to try the Boardwalk at night with your 4 yr old. They have outdoor carnival type games, you can rent a Surrey bike (I think that's what they are called) which seats 2, 4 or 6 people. The kids love just playing on the lawn there too. The Boardwalk does have 2 nightclubs that the kids can't go in but they can go into ESPN which has a game room. If you time it right, you can also see the higher Illuminations fireworks.