Lindsay starts to eat her bowl of Vector cereal before Lucas has poured the milk onto it. No one who was going to eat cereal with milk would start by eating it dry.
When the brick comes through the kitchen window, Darby picks it up in her bare hand to look at it. As an ex-police officer, she should be well aware that she shouldn't touch evidence with her bare hands, in case there are fingerprints. In the next scene a cop inspects it and indeed is wearing gloves.