You can take him to Tikes Peak at BB and he can ride alone on the waterslides there. My son has done it for the last 2 years (he is now 4) and this trip was my daughters first doing the "bigger" water slides at Tikes Peak (she is 2 1/2). There a a few types of slides at Tikes Peak. There are two slides that they have to do alone - one where they sit right on the slide and another where they sit on a tube. I was nervous about my daughter doing them this year but she really wanted to and there were some kids even smaller than her riding them. So off she went (I brought her to the top and my husband waited at the bottom) and she rode them over and over and over! They are pretty small and are short in duration. There is also a set of really small water slides that are really short (like a Little Tikes outdoor slide size). There is also a set of slides behind the pool area of Tikes Peak where your son and ride down on your lap.
We love BB just for this reason, the kids have so much fun in this area. There are also pop up jets here and a small wading type pool with little floats for them to climb on.