Help with the name of this book?

Ok so I read this book about 6 years ago, it was a murder/thriller type genre. What I remember from it is this woman (I think she was a babysitter or nanny) would give babies some kind of sleeping medicine to make it look like they were dead and then steal them or something like that because she wanted her own baby. I know this is super vague but if anyone has any idea what book this might be it would be great, Thanks