Two older boys sexually assaulted me in a mixed school changing room. I was eight and I continue to suffer the psychological consequences, including self-harm, depression, fear of biological males, and suicide attempts. I never want another little girl to go through that.
Had I known that children over eight were meant to keep out of mixed changing rooms, I might have screamed, fled, or fought back. Not sat wrestling with a broken shoe lace whilst they walked up to me and surrounded me. I wish I had known my rights.
I demand that the right to single-sex changing rooms and toilets at schools be extended to children of all ages, not just those over eight. I demand that girls be taught that no boy is allowed in the girls loos and changing rooms and be taught that they have the right to challenge and defend their spaces.
When girls are taught that they must accept boys who claim to be girls into their spaces, they are taught not to challenge boys "because they might be trans". They are taught not to defend their spaces because "it's transphobic" to do so. This makes it easier for boys and men to enter girls' spaces unchallenged. It makes it easier for boys and men to sexually assault girls. It increases the number of girls and women suffering the life-long psychological sequelae of male entitlement.
Let the trans child have the private changing room. This respects their desire not to be treated like the other children of their own sex whilst respecting the right to single-sex spaces of the children of the opposite sex. Most gender dysphoric people don't want people of either sex to see their pre-transition bodies anyway.