OMG! That one brought back some very nasty memories.
In 1972 my then 2 1/2 year old daughter and several other children were playing around a neighbor's pool. I sat on the sidelines with two other mothers, watching the kids. At one point I got up to put my newborn into the stroller over in the shade and when I turned back my older child was floating face down in the deep end. Yes, it does happen that fast.
The other kids thought she was playing, none of the adults had noticed, maybe because each was watching her own. The men were doing guy things in the garage.
I took a flying leap, and I'm not kidding, from the steps to where Shari floated. I mean, I grew wings! I got her out of the water and one of the fathers, alerted by my screams, rolled her over and pounded her back. She sputtered, puked up water, and was fine. I, OTOH, was not fine at all and seeing that little boy float in the pool brought it all back.
What an excellent program! Had that been around back in the day I would certainly have enrolled myself and the little ones.