The parents in the film, played by Stephen Dunham and Alexondra Lee were a real life married couple. Sadly, Stephen Dunham died on September 14, 2012 of a heart attack, shortly before the film was theatrically released.
Brady Allen's character, Robbie, was named after Robbie Mannheim, a child that in 1959 was an alleged victim of an evil possession and he had an exorcism to save his life.
The first actual sequel in the series. The prior two sequels were prequels.
The chronological order of the films is: Paranormal Activity 3 (2011), Paranormal Activity 2 (2010),Paranormal Activity (2007), Paranormal Activity 4 (2012), Paranormal Activity: The Marked Ones (2014) and Paranormal Activity: The Ghost Dimension (2015).