Is this a good, simple idea for a book?

It sounds intresting enough even though the whole 'Evil Stepmother ' thing sounds a little cliched and I think I've watch a movie very similar to this but this all depends on you and your target audience. Are you writing for kids, teens or adults (primarily of course)? I think it could be a good Idea depending on where this idea goes from here. Expand on it and let it grow into your vision.