I never saw the original "The Bad Seed", but I recall my mother telling me about it and how chilling Patty McCormack's performance was. It is possible that just hearing about the original clouded my judgment, but here's my opinion.
In this version, Carrie Wells was anything but chilling, she was just plain whiny, spoiled, and annoying. I never felt disturbed while watching her, I just felt irritated. She never came across as "evil", just bratty. I just kept wanting to slap the you know what out of her.
I didn't find any of the other actors to be all that impressive in their roles, either.