First, 4 is alot different than 9. If your going to change a 9 yr. old boy in a women's dressing room, I have a problem with that. At 4 they are just still a baby, 9 is different. But let me say that my now 6 yr. old DD would probably not like your DS 4 in there either if she is changing. She is just beginning to notice boys are different than girls. She would probably end up in tears and not change, even after I explained why you were changing him and protecting him. I would have ended up in the stall with her and my DD 9. Girls this age are just this way, no matter how much you explain it, they are still young and just becoming aware of all the differences. I think the polite thing for you to do is take him to the stall if the girls are trying to change. I don't think the girls mind seeing a naked 4 yr. old boy, but they don't want him to see them naked. In my opinion you should respect that. It is a girls restroom. Girls squeal, at least mine do from time to time. Don't know where they learn it, but they do.