It's been months, and Joker or any other villains haven't been causing trouble, which is good since Gotham's been empty.

So people thought

It was unexpected for Joker, Harley Quinn and Joker's army of goons to attack Gotham Daycare Center. There was a shooting. Bruce or anyone wasn't expecting him to attack to be at the same daycare his youngest kid goes to

Kids were running around the school screaming or crying that they wanted their mom or dad, or both, teachers were trying to get them to safety, there was laughing gas spreading around the daycare, and the heroes haven't arrived yet.

Joker targeted a school where you go.