Double barrelling a surname.

Ey? So you want reasons to do double barrell?

@Jody the father's hasn't been in the children's lives for 6 years now. And I want to add my name to the children's name.

You'd likely need permission from the father despite the situation. You could look to notify the children's school so they can add a "known as" name to their records so exercise books are adapted , but anything formal would still be using the name from their birth certificate.

@Sarah sadly, I do not have any way of contacting him, other than going the court route to get permission off them.