I am fond of Coral World when children visit us. There is a touch pool, feeding the stingrays, petting the shark and many other exhibits that kids (and adults) enjoy.

If you go to (as of this wriing) page 3 on this forum you'll find a similar post from just a little over a week ago with a bunch of suggestions which might give you ideas.

I agree Coral World is a great place to take kids. Mountain Top is beautiful for everyone, there is fun shopping, an incredible view and world famous banana daiquiri's. Don't know where you are staying but a calypso show at any of the resorts is great for the fam too. There is something called Nautilus, I've never been, but it's a small sub that takes you under shallow water to look at the sea, your son might enjoy that.
Have fun!!