The kiddie pool area at Kidani is amazing -- spraying water, falling water, small water slide, etc. Some of it you'd need to be right there with him to keep him safe but a few things you could let him stroll around and explore. The main pool at Kidani is small and not nearly as nice as Jambo House's pool. I think the Kidani slide is better, but the pool itself is basic and pretty small. Jambo House's main pool has zero depth entry, a slide, and is much larger.
The Jambo House kiddie pool is just basic...nothing exciting, but you're able to utilize both pools when you stay at AKL so personally I'd want to stay at Jambo House due to convenience to the restaurants (esp The Mara) and make a little trip over to Kidani to swim. Or, you may be plenty happy with Jambo's pool offerings.
At the Jambo House pool there is an area where they keep flamingos along the backside of the pool...definitely check that out!