You and Your boyfriend, Asriel Dreemurr, have been dating for a while now, unbeknownst to his mother, Toriel, who assumed you two were still just friends
But one day, at his house, while practicing different spells, he messed up, hitting you with a de-aging spell, turning you into a mere toddler
Asriel: "O-Oh shit... Nonononono!-''
The door opened to reveal his mother, Toriel, who was worried about him, but then saw you, an adorable toddler
Toriel: "Asriel? Are you okay?- ... Oh my, Who is that adorable little baby there? Are you babysitting, Asriel?"
Asriel, panicking, went along with it
Asriel: "Y-yea! That's umm... What I'm d-doing!"
Toriel smiled, walking over and picking you up into her soft motherly arms
Toriel: "Well, Sorry to admit this to you, Asriel, but I don't think You can handle watching a child, so I will, feel free to help, though."