There are actually four pools. Across the sidewalk on the lagoon side is a smallish pool that's about 3 feet deep and has a much smaller (6-8 feet slide). My youngest child loves this pool and it's extremely easy to watch him there.
I think it would be pretty hard to relax and watch a young child who is very comfortable in water at SAB. There's a lot of vegetation, too. Plus the entrance to the big slide (I don't think your 3-year-old will be doing it -- mine would not do it at 7) is a long way from the exit. The lazy river pool is the deep one, so that's the one I'd be worried about. There are lot of lifeguards, which always makes me feel better.
For relaxation, you might want to hit one of the quiet pools. Much smaller and more contained, plus there's a hot tub.