A woman who knows the mother and the girl in the video alerted the local media. Their faces are blurred in the video to protect their identities.
A child psychologist found the fight tough to stomach.
"That's pretty overwhelming," said Dr. Russell Hyken, child psychologist. "Those are small children that really don't even understand what is going on. I mean one child is screaming and the other child continues to go after her. I'm thinking, what is going on here?"
Missouri's Department of Social Services isn't commenting on the case but its investigators have viewed the tape.