Cinderella effect

The Cinderella effect is a saying that describes the idea that bad things happen to children more often when an abusive or irresponsible stepparent is involved. Basically, it's like Cinderella in the old fairy tale, who was treated badly by her stepmother. The same idea is applied to real life - when a step-parent comes into a family and the parent isn't a good influence, the kids in the family can end up suffering in some way as a result.