I'd like to know where you get your data for the "most kids get plenty of swimming in 5 or 6 feet". What aged kids? With what swimming skills? How was the survey conducted? What were the criteria used to determine what "plenty of swimming" is?
Whether you are correct or not, you see, *I* don't get plenty of swimming in 5 or 6 feet of water. I like to swim with my children. My five year-old is also a good swimmer and although 5 to 6 feet is adequate for him (now), even at 5'4" it's rather shallow for me to do a descent tuck dive. I'd like to teach him someday, but I'm not cracking my head on the bottom of the pool to do so.
My five year-old loves diving to the bottom after various objects. Our three foot hot tub is pathetically shallow. Two more feet makes it a bit more exciting for now, but it won't be long before he's capable and interested in going deeper.
I agree 5 or 6 feet may be adequate, but who in the world wants to live with adequate when superior is possible?
Well, I can swim laps in the pool, so I know it is good for swimming. The swim team goes to age 18, and lots of the 18 year olds are on their high school swim teams. The public school has an award winning swim team.
I know the older kids have to swim 50 feet without stopping, and most of them do that in under 40 seconds.
The swim team practices last from 30 minutes for the 6 and unders, 45 minutes for the 6-10 year olds, and an hour for the 11-18 year olds. They swim laps continuously for that duration.
I figure if the pool is good for swimming laps like that than kids can get enough swimming in it. You can also dive in 6 feet of water, so my kids are learning how to dive.
All of my kids swim better than I did at their age, and I had access to a pool with a deep end and a diving board. My parents never signed me up for a swim team. The swim team is why my kids are good swimmers.