Hello, Heart. The other responses are technically true. Mainly used in the romantic sense. However, Ive heard people many times use something like this to just show extreme joy for someone. In your case maybe you are talking to one of your friends, you might say: "wow, did you meet so-and-so's baby?! so cute, he stole my heart!" and yes, in this context it makes most sense in the 3rd person. Saying it directly to the baby isnt as commonly used. Hope this helps

Yes, you can say it. "You have stolen my heart" works better if you are actually talking to the baby because you talking about the present, not the past: "This is what HAS happened. You HAVE stolen my heart." "Have" is present tense. You are not talking about something that happened in the past, like "Yesterday, thieves stole my wallet". I do not think of "to steal someone's heart" as a romantic expression. It happens to me all the time. People, and animals too, wander off with my heart. I am constantly defending my heart. I see birds flying in the sky carrying my heart away. The metaphors you choose to use to describe your own life and your own feelings are personal. You can select them yourself. They do not need to be the same ones that other people commonly use. It is not possible to consider "you stole my heart" (to a baby) to be inappropriate or offensive in any way.

It's more of a romantic expression and It doesn't necessarily mean that someone is cute. It's often used to express an emotional connection. 😄

You can say it if you want to, but it doesn't really express the idea that you think the baby is cute. It's used to express the beginning of a more like term, emotional connection, so it could be said about/to a baby you have a long-term relationship with - your own child, niece or nephew, etc. If you said this to/about a baby you don't have a long-term relationship with, it'd be assumed to be hyperbole. If you want to address the baby in this way, you'd say, "You have stolen my heart!" Of course, the baby won't understand but the parent will, and might feel flattered.

We use this expression in romantic or affectionate way. Like for express your sudden affection or love for someone and you suddenly fall for something.