The separate children’s area thing is confusing in itself, but for context (having seen the facilities) there are two separate children’s areas, one in the males and the other in the females. In reality it’s a similar communal area around a corner/partition from the ‘main’ changing area – my wife tells me it’s the same situation in the females. Adults (by which I mean parents) can and do change in the children’s area, so it isn’t restricted to just a children’s changing zone.
This is a pool at a local gym, so I’m not sure if there are other family swim sessions at other times, with or without a gym membership. Maybe has something to do with the weird rules.