The first trailer stated their baby died and the doll was brought in to help his wife who couldn’t except the reality of losing a child.the previous trailer had a little more clarity on that. It seems like for some reason the “parents” get the fake baby. I’m not sure if they cannot have kids, lost a kid, or what. The husband appears to agree to it because it mentally helps the wife. They then hire a nanny to babysit the fake baby. Apparently the nanny’s past is dark.