Children do not need to be introduced to gender dysphoria or any aspect of transgenderism. All they need to learn is that if a boy wants to wear a pink frock and play with a dolly, that's fine. And if a girl wants to wear camo trousers and play football, that's fine. And that is all they need to learn about gender at 4-5yo.
All the school needed to do to avoid accusations of discrimination was to accept the confused child as he chose to present himself, not to impose a dubious and contentious ideology upon the pupils.
I applaud those parents for voting with their feet.