Why the fuck do I have to watch my coworker's shitty kid?

Coworker leaves work early, kid's mom wasn't home yet. Kid is now running around the office and destroying shit while the rest of us have to work. Why does the rest of us have to pick up the slack and miss work just to babysit an unattended minor?? Also, why is our office now a fucking day care? I've called security but our manager said we have to let the kid stay. Fuck this.