It seems the talk is now about SN use of changing rooms, which I have not much to say about. Going back to OP though and a lot of comments from the beginning, I have to say that at least some 8+ year old boys DO look at breasts. They certainly were keen on climbing up on cubicles in my local pool to look over, to look under the divisions in the closed off shower cubicles (some were open, some were closed) when I was younger. Often their mothers were busy with younger siblings and were letting the boys shower and then come to get changed with them, or once they were changed and mum was still dealing with sibling, they started the cubicle climbing. Their mother, with a crying toddler, trying not to drop anything on the wet floor, herself still dripping wet and in swimsuit couldn't possibly keep an eye on the boys.
I can say that every single time I went swimming aged 12+ (early developer!) I had boys looking at me. It was NOT comfortable and it definitely reduced the frequency I did something I really enjoyed.
Incidentally, also every time I went swimming, boys aged about 8+ who swim with goggles, often would swim underwater, towards me, eyes trained on my chest. I soon got used to kicking or hitting them as we passed, but this too was not welcome.
Additionally, my local pool (olympic size) had a separate diving pool. Every time I started diving, there would be a few boys who would either linger in the pool just a little longer than necessary, to try and get a look down my top as I swam up after the dive (the lifeguards would usually put an end to that pretty quickly as they were strict about getting out of the pool immediately for safety reasons), or stand at the railing beside the ladder to gawp when I got out of the pool.
And I can assure you, I was not a hottie! They were purely there for my boobs.
I'd say that from what I experienced from age 12 to 18 in my local pool, boys aged 8+ do look at boobs, but NOT those of women they think are about the same age as their mothers. The boys that are looking are not stupid, they know they're more likely to get in trouble from someone who looks like they could have authority.
So, my vote goes for family changing rooms and no unaccompanied boys in ladies' changing rooms (whether cubicles or open) no matter what their age and staff who actually enforce the rules.
Oh, and in this day and age, it should go without saying that SN are catered for in public pools, whether for adults or children.