Whats that one movie called...?

At the beginning it shows a family of four, but it doesn't show their faces, and they have two kids that are twins and one of them is struggling to get in his high chair and one of them is really good so they give him more cheerios (lolol), so the parents strap the bad twin in and he scratches the mom and the mom slaps him...it's a horror movie, and I know that the bad twin grows up to be a serial killer.