Interview with a Vampire TV Series

I'm a few episodes behind

So my understanding is once you are turned into a vampire you stop aging at that moment

Is that what would have happened if Louis turned the baby? I'm assuming the baby would stop growing but would it mature mentally, to think and talk? (into a baby Herman thing) or just forever a baby, that needs blood?

In the book, Claudia is like...five or six. Her mind ages but she never gains the true maturity that comes with physical age. It costs her dearly in the end.

IIRC were a vampire to turn a baby, it'd go completely insane in short order as its mind matures but it never gains full motor control of its body. Imagine Baby Herman, but he can't reliably get that stogie to his mouth and he still craps himself.