Well, I see people taking young boys (younger than 10?) into the ladies room all the time and I think nothing of it. I certainly don't like it when they 'peek' but that actually applies to *all* children who do that, of either gender and I don't think I've ever seen a kid older than three or four do that. My 5 yo dd will comment every time we see a boy in the ladies room, but I just remind her that the men's/ladies' room rules only apply to adults. Boys with their moms have to go into the ladies room in public to keep them safe. My dh will not take the girls into the men's room anymore - he thinks they are too old b/c of the lack of privacy so he will send myy dds into the ladies room together, if I'm not there (they are 8 and 5). Unfortunately, I think girls can safely go into a ladies room alone at a younger age than young boys can go into the mens room alone.
Sorry, moms of boys, I don't like to change in the locker room with boys over 5 in there. I sympathize with your situation and would like to see *all* gyms offer a family changing area to address the situation. Because I know what kind of bind moms can be in with this issue, when I confront this situation (an older boy in a locker room at the pool where I am going to have to take off my bathing suit) I will either wait until mom or son are done and gone or I'll slip into a bathroom stall to get changed. One locker room we used to go to had one row of lockers reserved for moms with older boys, but there was still a problem with some of the boys peeking around the lockers. I remember a mom or two on the locker room thread basically saying, 'too bad, my son's safety is more important than your modesty' in regards to this issue, but I personally think if you have to be brininging your boy into a room where women may need to take off all their clothing, you *must* teach them not to look and stare at the women. It's only common courtesy and respect for the same boundaries you are worried about with your sons. I definitely do not think the solution is to send those little boys into the locker room alone, though. Ultimately, gyms needs to convert some of their space for family use.
Sorry for rambling - I've just had those thoughts at the back of my mind since I read the other two threads.