I'm a trans woman. I wish I could tell you what it's like, but analogies always seem to fail. No one understood that I was really a girl. I had to have my childhood as a boy. It was not what I wanted or needed. Trans kids today have had the gift of some of their childhood in their gender. I have seen these kids have the fun I never could quite let myself have as child, lest someone find out I "thought I was a girl".

Let trans kids be kids. If a person is bothered by someone simply changing in a locker room or using a restroom, most likely in a stall, they should find somewhere where they feel safe. Forcing the group that is receiving unwarranted bigotry and hate speech to call attention to their differences is not the answer. Let trans kids change where they feel comfortable (most likely somewhere private), most of the trans kids I have met don't drink anything until they get home from school, because they are afraid to pee. Let sensitive kids change where they feel comfortable (most likely somewhere private). And, let people who have no issues change where they may. Using a restroom is very similar. High school restrooms are often unsafe, with vaping, smoking, and other illicit activities taking place. 

Athletics is a difficult question. There are a myriad factors that go into making someone a good athlete. Testosterone is just one factor. Drive, ability to exercise, desire, competitiveness, size, and so many other factors go into whether a person is good at a sport. If a trans girl has gone through male puberty but has little to no testosterone in their body we don't know the complete story, there are not enough studies to understand the entire impact. A trans girl who has never gone through male puberty has very little extra advantage, and that is probably offset by being dehydrated because they are afraid to go to the restroom. High school is a time to have fun with sports, not worry about the few scholarships and high-level awards out there. Let the trans kids play.