Baby Battlemon are the first form in the Battlemon evolutionary line. The evolutionary line is as follows:
Baby --> Child --> Adult --> Champion --> Ultra --> Omega
Babies are the Battlemon when they first hatch. After a while they'll evolve into the Child form. For instance Catemon, a Baby Battlemon, will evolve into Clawman, the Child form.
Here is the way it works with Catemon
Catemon --> Clawmon --> Meowmon --> Persiamon -->Sharpclawmon --> Thornclawmon.