To me, a 12 year old boy should go to he men's room. If he needs help, his mother should accompany him. I can't imagine any group of men getting concerned over this. Would be much less of an issue for the mother to see the opposite gender undressed than for the 12 year old.
My wife claims most restroom designers are men. They put the same number of toilet stalls in both restrooms, then add an equal number of urinals to the men's. Recently I was in a campground bath house, just getting out of a shower when a woman called in the door, asking if she could come in and use the toilet, emergency and the women's room was full. One of the guys yelled for her to enter, which she did, entered one of the stalls and took care of her business. As she started to leave, one of the guys told her not to forget to wash her hands. The comment broke any tension in the room as she returned to a sink and washed. Then with a "thanks guys" she was out the door.
The situation didn't seem to cause anyone a problem, and should work just as well for a woman with a dependent needs boy.