I saw a movie when I was little. A woman hits a little boy with her car. The little boy took her home. He then turned out to have his whole family under his control. His sister locked in her room with her mouth nailed shut. The family ate only junk food . Might be a tales from the crypt creep-show flick.
That is one of four stories in Twilight Zone: The Movie from 1983.
As IMDB plot summary describes: "a young woman on the road gives a ride to a mysterious 10-year-old boy to his house and ends up trapped with other people in an alternate reality created by the boy's imagination."
Here's the original 1961 episode of Twilight Zone, also on IMDB.
I recall the actor who played the boy went on to star as Will Robinson in Lost In Space. IMDB confirms, actor Bill Mumy. I recall the boy had a line while foisting his evil on some helpless guy "You're a bad man! You're a very bad man!" as the guy dies a slow painful death or something.
I've seen versions of this story in multiple places, including a episode of Supernatural if I recall right.