We have similar at our local pool.
It's an open plan, communal, female change area. There are cubicles, but they are tiny, and there are very few, most without curtains anyway, and the few doors are broken.
I have noticed more and more women bringing their older boys in, and not always to get them changed. Sometimes as a shortcut to the pool, sometimes to wait while their sisters are changed, and on one occasion, to use the loo. The mum actually covered the childs eyes and told him not to look while she walked him through the change room (toilets are at opposite end to the door).
Now, I'm no prude, and I really don't care if a young boy wants to look at my wobbly bits. But there are a lot of teenage and young pre-teen girls getting changed in there. Often they're in groups getting changed after swimming training. My DD is only 10, but is starting to notice if older boys are in and getting self conscious, trying to cover up while she changes. These girls should be able to change openly in a female change room, or we will end up with a generation of girls who don't know what other womens bodies look like and feel they have to hide their own.
So yes, I think it's wrong to take boys older than 8 in a womens change room. DD has been able to use it by herself form 8 when DH takes her training, she gets changed with her friends and they all stick together.
There are separate accessible change rooms if you really need to take your opposite sex child with you.
Which reminds me, there is a vulnerable young special needs girl, post puberty, uses the change room. To see 11 year old boys gawping at her makes me very uncomfortable indeed.
I'm never sure whether to say anything. I've complained to staff but they really don't care about the pool changing. If it were their precious gym users changing they'd do something.