Daz has a Millennium Baby and Millennium Baby 3.  The original Millennium baby looks like a baby.  The Millennium Baby 3 looks more like a toddler to me.

Both are naked and you can add diapers or various types of clothing.  There are even character addon packages for them available so you can change the look of the infant.  It's a unisex baby (boy actually). But if you want it to be a girl you just have to hide the little bits, hehe

Also, there really isn't all that much out there for the babies, but Poser World has quite the selection of baby clothing and you will probably find some at Daz, Poser Pros and here in the MP.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi