Two days ago I adopted one. Her name is Amélie and she looks adorable. Woot woot, my Barbie has her own perfect baby now, I "played" with her for hours. As breed-able pets are a huge success in SL, Zooby added a comparable system to their babies.
Bottles, diapers, baby wash, furniture and many other accessories allow you to keep your baby happy and save up tokens to pay for their toys. To "level" up the baby you need to buy stars and apply it, your baby learns something new as soon as the time period of the star passes. More expensive stars speed up that process.
She makes cute noises and has none of the annoying things rl babies do: crying, drooling, smelly poo. It's a lot of fun, but it's a true money sink. Everything is heavily overpriced, some things are just ridiculous, like the Baby Snuggle Mat, 600L$ for a no-copy sculpty mat with an ugly texture, 4 poseballs with hover txt (i mean 2012 and poseballs wih hovertxt?). But is a business and they own the market so if you decide to make your avatar a parent make sure you got some cash to spend.