I teach swimming at my local Y now, and our facility even has special locker rooms for mother-daughter and father-son. No adult is allowed to use them unless accompanied by his or her child. Heck, if, in the middle of a class, a child has to go to the bathroom, one of the teachers of the same sex has to accompany the child, not to let the child go in alone. Oh, and parents are not allowed to leave the building to run errands, but rather have to stay in the lobby, behind the glass through which they can observe the class.
We take extreme care at the end of each lesson to make sure every child is paired up with the correct adult. All of those "filtering issues" have apparently been resolved, because even people with the longest hair aren't required to wear a swimcap.
There's a lot more social awareness now too, in the sense that they won't pair up a three-year-old beginner with an eight-year-old, for example. Therefore, you can get a class of 8-10-year-olds at a wide variety of ability levels and somehow have to make it work, from those who can do a little freestyle to those who are still afraid to put their face in the water.
Does anyone else remember the instructors as being much more out of the pool, on the sidelines, than they are today? We wouldn't be caught dead nowadays, not being in there with them. I seem to remember, esp. at the YMCA, the coaches just standing on the sidelines.