Paranormal Activity 3

In 2005, Katie delivers a box of old videotapes to her pregnant sister Kristi, and her husband Daniel Rey, which holds footage of young Katie and Kristi with their mother, Julie, and her boyfriend Dennis. A year later, Kristi and Daniel's house is ransacked and the tapes are missing.
In 1988, a young Katie and Kristi are living with their mother Julie and her boyfriend Dennis. Dennis notices that since Kristi's imaginary friend Toby appeared, strange things have been happening around the house. Dennis and Julie attempt to make a sex tape, but are interrupted by an earthquake. The camera shows dust fall from the ceiling and land on an invisible figure in the room. While reviewing the footage, Dennis notices the strange incident. His friend Randy suggests that Dennis place cameras throughout the house to capture any other incidents. That night in the girls' bedroom, Kristi wakes up and talks to someone off-camera. When Dennis questions her the following day, Kristi tells him it was Toby.
Dennis and Julie later hire a babysitter named Lisa to watch the kids, but she abruptly leaves after experiencing paranormal occurrences herself. Dennis discovers a strange symbol in the girls' closet, and later finds the same symbol in a book about demonology. When Kristi becomes ill, Julie and Dennis take her to the hospital. Katie is left home with Randy, and they play Bloody Mary in the girls' bathroom. When nothing happens, Katie insists they try again. Randy is then attacked and discovers a large scratch on his torso. They try to leave the bathroom, but a black figure moves past the door. The second time they try to leave, furniture is violently flung across the room. After Julie and Dennis return, Randy quickly leaves, warning that whatever they're dealing with is dangerous. Dennis tells Julie that the symbol he found in the girls' room belonged to a witches' coven that brainwashed girls of child-bearing age into having sons, and then force them to give up their sons; they would not remember anything afterward. Julie dismisses his claim, and instead argues with Dennis.
The invisible demon terrorizes Katie and Kristi, harming Katie until Kristi agrees to do what it asks. The next day, Kristi asks her mother to take them to her grandmother Lois's house in Moorpark, California, but she refuses. After Julie encounters frightening activity herself, she agrees to go to Lois's home. Dennis sets up another camera in their new bedroom. At 1 am, they are awoken by loud disturbances and Julie goes to investigate. When she fails to return, Dennis goes to look for her. He calls for Julie and the girls but there is apparently no one there. Downstairs, Dennis notices a human silhouette behind a curtain, but when he looks there is no one there. He finds occult imagery on the walls, including the symbol from the girls' room, which had been concealed behind paintings. Dennis enters the garage and discovers several women, including Lois, dressed in all black. He flees back to the house, with the women in pursuit. In the house, he finds Julie at the top of the stairs. As he approaches her, he sees that her limp body is levitating above the ground. Her body is thrown at Dennis, knocking him down the stairs. He sees Kristi, and hides with her in a closet. The demon growls and bangs on the door, but eventually leaves.
Dennis and Kristi leave the closet and walk into the kitchen. In the window, Dennis sees the women outside in the garden, circling around a bonfire. They find Katie crying by the stairs near Julie's body. Dennis approaches Katie from behind, but when he places his hand on her shoulder, Katie turns around and unleashes a demonic scream that throws him to the other side of the room, injuring his leg. Katie flees and Dennis tries to crawl toward Julie's body. Lois stands in his way, and Dennis's body is violently contorted, killing him. Lois then beckons to Kristi and Katie and says "Let's get ready". As they head upstairs, Kristi calls for Toby and then the camera goes to static and black after low growling sounds.

Question: How many children are being watched?
Answer: two children