Brad Pitt & Angelina Jolie-- Cop Cars, Helicopter Race to Hollywood Hills Mansion

DON'T PUSH THAT BUTTON ... a lesson learned the hard way by one of Brad Pitt and Angelina Jolie's kids ... who accidentally pushed a "panic alarm" inside their house last night that attracted a police FRENZY ... TMZ has learned.

Law enforcement sources tell TMZ ... cops were called Friday night to casa de Pitt around 9:00 PM after an alarm went off at their Hollywood Hills home.

Our sources say police arrived to the scene -- via both car AND helicopter -- only to be told it was all a big mistake. We're told they spoke to a nanny (Brad and Angie weren't there) who informed them about the child's mishap.