Sago, I did post earlier about this but the leisure centres themselves have rules about children being accompanied under a certain age and it is a direct result of safeguarding. It isn't (or wasn't) unusual for youngsters to be sexually assaulted in swimming pools. Ask anyone who has ever worked in a leisure centre, they know who these men are.
As for dressing/undressing, I do think that is a bit odd. You used to be asked to get them used to putting their PE kit on and off before they started school. Mine had no problem though as they used to and still do change their clothes several times a day
I learned to swim, many years ago, at an old Victorian swimming pool. The cubicles were round the pool on three walls. No issues with boys or girls being with a parent of the opposite sex as anyone could use a cubicle. They weren't the flimsy metal type, the were proper little rooms, brick walls, heavy wooden door.
The life guards were round the pool so you never felt isolated like the modern changing rooms with no supervision.
The Victorians got some stuff right in my opinion.