Her son's initial reaction just makes Toriel's expression drop, a hand pressing against her chest. Asriel, Flowey- this child has lived so many life times and seen too much. This is just another scar for him, it makes Toriel's anger towards the Captains grow all the stronger.

"I did tell you I would return." She takes a few steps forward, crouching low and carefully pulling Asriel into her grasp. She hasn't missed the glass across her son's chest, so her touch is tender and gentle.