The first time Mother calls 911 and hangs up after it was answered, the 911 dispatcher doesn't attempt to call back. In reality, 911 would immediately call back on a hang up call.
When Mother breastfeeds her baby, during one shot, she has a scar on her forehead. During the next shot, there is not a blemish on her face.
After one of the sons is murdered, the Mother fails to call 911. All she does is clean up the crime scene and dispose of the evidence, making her complicit in the crime, something her character does not demonstrate in any other sense throughout the movie. Although the household is descending into bedlam, and her lack of control became increasingly uncomfortable for the viewer, the fact she did not protest the murder felt ill placed within the broader context of the film.