Not to mention some of those kids may end up changing their names at some point if they get married and decide to take their partner’s last name.
Nice twist: The father of my wife owned {newlastname}.de since the dawn of the internet. So I'm still fine on that front. ;)
I've successfully renamed an old account with an email address I no longer liked. It works quite well on everything 1st party, but does have the potential of causing issues with OAuth on poorly-coded websites that key on email instead of user ID (ie. most of them). You do get to keep your old email address though, so it still ends up working fine in practice.