It has a little baby that's evil and nobody believes the mom. She has brown curly hair. But the baby is evil and the lady shoots him at some point and his head enlarges and stuff. That pretty much all I can remember except for the fact that he had sharp teeth.

You might want to see this article, it's a list of movies with evil babies in them.

Maybe the one you're looking for is there.

http://www.avclub.com/articles/he-has-his-fathers-eyes-21-creepy-babies-in-film-a,40679/