Parents don't have that right, their children are also members of our society which entitles them, philosophically at least, to our collective protection and care. The rights by which trans affirming parents are in the clear is the individual rights of their child not their own parental rights.

Exactly.

I agree philosophically, but that’s not legally helpful when figuring out what’s best for a kid. The legal concept of parental rights assumes that parents are most likely to know what’s best for the child. This becomes less true as a kid grows but we assume as a society it’s true until they are 18.