well, we're not parents yet, but i'd be surprised if a tank in his room would keep him awake or encourage bed wetting.. for one thing, the little plastic aquarium toys seem to be popular in nurseries and thought to be soothing. Try getting comfy and just lie there watching an aquarium for a while and it should give you an idea how it can be relaxing to us humans, even when children or babies.
With a quiet filter and full tank and a small air stone, you will have very little in the way of water noises.
Best of luck with your new baby and when we have kids, we plan to have a small aquarium within view with some very colorful guppies in it, everything done up big on color for visual stimulation.. bright, colorful flat marbles for the substrata, bright silk/plastic plants and caves.

maybe even with a oceans sounds cd on loop real soft playing.
