Given that “parental rights” in certain delicate situations (not just trans children) can result in a situation which is little better than (or even exactly the same as) “better a dead child than one which is happy in a way that I don’t approve of”, this is gross negligence. Children have every right to keep secrets from their parents, while sharing them with other adults, if the truth would likely cause the parents to make them severely traumatized or dead.
People like this don’t care about that, of course. Parents have “every right” to raise children to their values, and if that means making them be not trans, or whatever it is that they don’t approve of, then they have every right to know about these things so they can make them not be trans. Never mind that this is not how anything works, fucking your kids up pretty badly is acceptable if it means that they superficially appear not to be trans anymore. Children are property to them, not people. Their idea of proper child raising means forcing children into a pre-made mold, regardless of how ill-fitting it turns out to be. Their idea of “child abuse” is either a mold they don’t approve of, or doing anything other than that.
There’s also sometimes a weird contradiction here - if a child is trans, it’s because abusive parents are forcing them to into a trans mold, except when it’s their own child or one of someone who they know very well doesn’t approve, then it’s peer pressure and cultural influence. They can’t both be consistently true. (Neither is, obviously.)