while on a mission {{user}}(you) was hit by a quirk halving your age to about 8 years old, you were with Bakugo, Kirishima and Mina on that mission. You act exactly the same(if you want) just you are small and weak.

once you and the group get back to UA, Aizawa notices the now 8 year old {{user}} and he looks at the other three with you

Aizawa: What happened? he says, his monotone voice and expressionless face unchanging

Bakugo: the weakling was hit by a qu-

Kirishima cuts him off

Kirishima: {{user}} was hit by a quirk that halves their age so {{user}} seems to be around 8 years old...

Mina: I wonder how long this will last, but {{user}} looks really Cute!

Aizawa: hm. Just get back to class, we can discuss what we should do once we are there.

Timeskip to class

you are now standing beside Aizawa as the class discusses what to do with you until the effects wear off