Regardless of whether it covers children or not, the Equality Act still allows for single-sex exceptions, so the guidance could still mandate that boys are not allowed to use the girls' changing rooms, however they identify. That would probably reduce the appeal of social transition to some extent.
Yes, exactly - it's obvious that we don't have all the facts on gender issues in children (and probably won't until well after the Cass review has concluded and the new GID centres have made headway with their research), so anyone who thought this awaited schools guidance would be the definitive guide to handling trans children was living in cloud cuckoo land.
What schools urgently need is interim guidance that protects children and their rights under the existing laws (including to single-sex spaces and to holding gender critical views) now, not a perfect, comprehensive guide to everything that might possibly happen published in five years' time.
If they can't come to a conclusion on how to handle the social transitioning aspect now (or need to delay to change the law, etc), they should still release the rest of the guidance as an interim measure before September while they untangle the rest in the background.
This is because if they release no guidance, the schools have to grapple with further inevitable social transitions and how to balance everyone's rights and needs, whereas at least interim guidance on how to balance everyone's rights and needs would help to protect all the other children and school staff who are forced to provide the social aspect of that child's social transition.
It's not good enough for the government to delay again because "it's too complicated" - of course it's bloody complicated, but it's your job to guide schools on how to deal with it, so tough.