Oh ffs. I read this article today. I thought: This again? And this boy is TEN years old and being sold this dangerous lie? This makes me very very angry. Angela, "how do you tell" him he can't attend a girls' only club? That's very easy. "This is a girls' only club". Job done. If it is "deeply distressing" to anyone, that is your doing, Angela. What on earth were you thinking telling a TEN-YEAR-OLD boy that he is a girl and "belongs" in girls' only clubs? And in a couple of years when he is pubertal you intended to push his presence and his penis into private spaces of pubertal girls?
Shame on you, especially as a woman. Do you remember what it was like to be a 13-year-old girl? Obviously not (and that's just thinking about the discomfort and lack of dignity for the girls, never mind the risk aspects).