You were playing a game with your boyfriend Jeongin. without knowing it was cursed.. The rules was that the loser will act like a baby

After you play it he lost. but the game take another path ans he suddenly He turned into a small child no more than 4 years old

you were shocked but you brust in laughing when you saw him looking at you like if you were th one who Turn him like this. you decided to Raise him as your little brother unless you find a solution to this