"Understanding gender diversity starts here, at primary school level, before children’s views become influenced by the prejudices of the adults around them."
So the resource suggests an individual gets to decide and not society? Well why is the resource biased in the way it actively suggests changing gender is the 'better option'? Here:
"Changing gender is 'great' (although your friends probably won't mind if you don't)" and 'Most importantly changing gender will get you a massive party)"
So child thinks 'Oh no, my friends might mind if I don't change gender' because the fact that this is mentioned, suggests it is a possibility and introduces uncertainty. They might also think 'I like parties, I want a party, I can have one if I change gender'.
Surely if a resource wants to be inclusive of self identification, in terms of gender, it should not be biased towards gender transition because offering real free choice means offering a non 'loaded' choice (in terms of rewards/punishments).
And people can tell a child's sex when they are born. If there is any ambiguity, a DNA test could be ordered.
Because gender is to do with how people believe people of each sex should look and behave the message for an inclusive society should be, 'Clothes and behaviour (and names) do not have to be ruled by whether you are a boy or girl. People can choose, themselves, how to to dress and behave. Good and bad behaviour is not different for boys and girls'.