While filming at the dark house where Adam and Shane search for the suspects, there was a real gang nearby who got used to them being there, thinking they were only actors, but there were a few real officers with them who carried out a real arrest during a drug deal while filming was going on.
While filming the arrest early in the film, the actors who played the gangsters were actually sharing their faith with local people in-between takes, including the two that pass by on bikes while they're driving to the house.
The Taser gun used in the arrest was real. It wasn't fully charged so it wouldn't hurt anyone, but while filming, it actually recoiled and shocked Shane Fuller (Kevin Downes), not the gangster. He fell down and cut his hand on a brick.
The baby in the truck at the beginning was Ken Bevel's actual son. They were not expecting him to be crying when they opened the door, but it fit perfectly for the scene. In the audio commentary Stephen Kendrick says "there was nobody in the car prompting him to cry, we all were shocked and got chills that day when he opened the truck and the baby cried like that, it was GOD directing that portion of the scene, we were blown away by that."
The scene that Adam Mitchell is watching on TV (with his daughter in his lap) is from the house fire in Fireproof (2008).