Ohhhhh boy....
I can understand the reason behind that, they rather not have young children asking questions about grown up issues that a lot of idiots would like pushed into very young children's education, when they aren't ready to learn about such things and stepping over parents right to chose when their children learn about such things
Based on what the people who find it difficult say when they give any detail at all, I'd go even farther than that.If a child can understand "boy" and "girl" then they can understand "nonbinary." In fact, kids are probably more likely to get the concept as they haven't had decades to galvanize old (and antiquated) gender norms in their minds, where everything has to fall into group M or group F, and those groups have very rigid (and untrue) definitions.
If that side of the conversation ends where it is, then it is fine. Any further dive into the topic should be taken to P&R though.As much as this is about Earthspark, it really belongs in the politics forum.
---Dave