Plot hole: When Mike Walker is out looking for his son Connor calls Satch and asks, "What's up with Mike?". She couldn't know that there was anything up with him, she left before he heard his son was missing. Had she called Walker on his cell, he would have explained what was going on, as he was very eager to tell her. Obviously a set-up so that Satch could tell her that the boy was missing.
Character mistake: When Walker and Satch are in the car looking for Walker's son, Walker tells Satch his son is 17. Afterward, when they are out on the streets, Walker asks some people if they have seen his 18-year old son.
Continuity mistake: When we first see Darren's sister coming out of the apartment she has a pram with her, but there's no baby in it, but in the next shot were we see her go back inside and up the stairs she is carrying her baby.