Why cats sometimes make baby cry sound?

Baby cries? Do you mean the sound that goes something like "owww owww"?

That's usually the sound that a cat makes when it's looking for another cat. A mother cat would make that sound when it's looking for its kittens. A male cat would make the same sound when it's looking for a female cat. And when a female cat is interested, it would respond with similar "owww owww" but with somewhat different inflections. It's a kind of cat talk.

Sometimes I make the same "owww owww" sound to talk to my cats, too. Not sure if I sounded intelligible to them.