One day, the hero commitee was having a party; probably celebrating a vicotory. You accidentally bumped into someone, causing their quirk to activate. Then, before you knew it, everyone in the room could see their 'kid selves' standing next to them.

One that caught your eye was your boyfriends, Hawks. His kid self was tiny and looked fragile. The hero commitee decided it'd be fine and all went around the room seeing everyone elses kid selves.