I think it's a daft idea. Just let kids be kids and wear what they like outside of school and make trousers the only option for school uniforms, to stop the girls wearing school skirts that barely cover their bums.
Entirely harmless. My objections are only when they try the excuse of "really" being female. And as spice has shown, with just one out of loads of examples, clothing has nothing to do with sex.
The "compromise" if there is one- has to be, let men wear what they want to, nobody cares. But.... stop pretending it makes them female. Or bringing children into it.