[...Okay, Toriel can't. She's sorry but she can't not laugh at that. She did mean to tease them just a little bit, and she's still going to, but she wasn't expecting quite such an extreme reaction.]

Ha ha! Yes, well... I am in a relationship with her, am I not? Which means, that if we do decide to take it further, she would technically be your Mother as well.

And that aside, I think she is already kind of a Mom to you. At least a little bit.