Continuity mistake: When Kevin is breaking into the window of his neighbour's house after the boy has shot himself, there is a statue of Mary that is there on the window sill, then the next shot it has fallen on the floor from the breaking window, and then the next shot it's back up again.
Continuity mistake: In the scene when Tom is digging in the backyard, he has no mud on his chest. Next shot cuts to Maggie talking to him, then cuts back to Tom, who now has mud on his chest. Next shot, back to Maggie and then back to Tom, and the mud is gone. This happens again in the next few shots between them with the mud appearing then disappearing.