I don't know how you feel about Foster, but if you're not into him (child Foster is also an energetic explorer), then I would love to tag Toriel with Karako, who is aging UP and will.... probably be no taller than her despite being a wholeass adult. (Well, his horns will be. But they don't count.)

He will be obscenely strong and very supportive of troublemaking children. So, you know, if she needs encouragement...