be someone's baby

be (one's) baby

1. To be a project or goal that one has initiated and is very devoted to realizing. That initiative is Cheryl's baby, so you know she's going to do everything she can to make it successful. Good help is hard to find when you're working on something that's your baby. No one cares about it as much as you do, unfortunately. That research project was my baby. How dare the committee just stop funding it?

2. To be one's cherished possession. That car is Mike's baby. If it gets a scratch, he'll be inconsolable. Please tell me you didn't mess with your brother's video game system. You know his Friendtendo is his baby. Mom can show you how to use the sewing machine—it's her baby, after all.

be someone's baby

If you say that something is someone's baby, you mean that they have created it or are responsible for it. He's open to ideas for the movie, but it's his baby. There's no doubt Fashion Week is her baby.

be someone's baby

(of a project) be instigated and developed by one particular person; be someone's creation or special concern. informal