Continuity mistake: After Mrs. Russo puts Justin and Max in the lair, she is wondering if she should put the big lock on the door or not. She decides not to and puts the lock down on the counter. Two shots later you see the lock is back on the door, but unlocked. You never see Mrs. Russo put the lock on the door.
Continuity mistake: When Harper makes all the apples fall down, there is one more left on the stand. When it switches to Alex and then switches back to the stand, there are no apples on it. In the next shot the one single apple has reappeared back on the stand, then disappears again in the next shot.