Factual error: You can tell that the "Brillo pad" Andrew eats is not real as Andrew would have been VERY ill due to the cleansing chemicals on the pad and the fact that the metal would have cut his mouth considerably. There was no blood, no foam coming out of his mouth (the box says Oxy action implying foam), and he keeps eating despite that the taste would have been horrible.
Revealing mistake: When Stewart is working on his laptop at the satellite dishes, it is very obvious that he cannot type. He is tapping the keyboard repeatedly with several fingers, without moving his hands.
Factual error: I used to cheer at major competitions like at the end of the movie. These competitons have VERY strict rules concerning music and acceptable moves. Carrie's cheer team would not have been allowed to compete with the song they use and some of the moves they do. They would have been considered vulgar/ inappropriate for their age group and the team would have been immediately disqualified.
Continuity mistake: When Malcolm/Big Momma goes to the beach, he is wearing a prosthetic bodysuit as we can see in shots of Big Momma in a bathing suit. He puts on a sun dress to cover up. Not long afterward, he chases Bishop down a pier and his mask comes off. We can see a heavier cloth bodysuit underneath the dress on his right shoulder, but Malcolm had no opportunity to change bodysuits.