During a battle between the Justice League and the magic side, Batman was unfortunate enough to be hit by an enemy curse. And, just like that, he became a child.
The Robins spent a long time panicking (?) about it.
To keep it under wraps, they and Alfred came to a decision:
They would send Batman to school.
Alfred: Just think of it as returning to your childhood, sir.
Bruce: ...
On his first day of school, he met a deskmate who was ridiculously handsome. Then...
Deskmate: Got plans?
Bruce: ...I guess?
Deskmate: Then let's go.
Bruce: Where?
Deskmate: Arkham.
Bruce: ?!
