Are you being forced to teach this? 
If this book actually pretends that George's genderfeelz mean he should be allowed in the girls' changing rooms, then I would make sure the kids know about biological facts, and that it is not possible to change sex.
You will also have to teach the basic facts about women's struggle for equality, i.e. the suffragettes, etc., so that the children have all the background knowledge.
I believe that more information is always a good thing. I went to school in Germany, and we were shown pieces of nazi propaganda movies in history class so we would know what they look like.
Knowing that trans people exist will not harm them in any way.
Being brainwashed into believing that there is such a thing as a female brain in a male body will harm them.
It depends on the book. But considering how far down the rabbit hole the UK is, I have little hope that the book is not an attempt to brainwash children.