H.W.
When my youngest was born, I had a 4 year old, 2 year old, and a newborn. The 4 year old was good to go in an inflatable suit, life jacket, or floaties. The 2 year old mostly sat on the steps of the pool (in the same type of gear) but I took a small inflatable pool to sit next to the pool so she could get in it. The baby was so small that he slept a lot; I drug out Ol' Faithful (the pack 'n play) and he slept in that under an umbrella. He was cool, and I could focus on the girls. It may mean taking extra gear, but I kept everything in the car so I didn't have to pack and re-pack every time. I also kept a beach bag stocked with floaties, towels, sunscreen, toys, and anything else we might need so that it was always ready to go. I never walked away for even a second; if the baby woke up, he was close enough for me to get to without having to take my eyes off the other two. The pack 'n play was the back up plan; if anything ever went wrong with them (and it never did) then I had a quick, safe spot to put him so that I would be free to tend to the girls. As he got a little older (a few months) we got a float with a shade and he floated around with us in that.