Unfortunately that's not quite the script, so for those of us taken unawares before we've understood trans identity politics what actually happens is more like this:
Mum, Dad, I think I'm transgender.
Oh! What does that mean?
I can't explain it.
...
Mum, Dad, I'm calling myself Petunia.
OK, Petunia, but we still see you as the man you are. You will always be the son we love, as you have been from the moment we met you.
Call me your daughter or you are a bigot. As a trans woman I don't associate with bigots. Why can't you be kind?
No, we're not prepared to be coerced into pretending you're our daughter. That would play havoc with our mental health.
Transphobes! You hate me and want me to be unhappy! Don't contact me or I will blame you for not respecting me.
OK, we will respect your request and minimise contact, but we love you and will occasionally message you, in the hope that our relationship can be rebuilt. That's likely to be a difficult painful process for us all, but we think you are worth that.
[What we fear, so hopefully untrue] You are not treating me as part of your family, so you obviously don't love me! [Maybe reality will reassert itself but in the meantime we are all in a state of ambiguous grief.]