The only baby defaults that seem to be working are from the creator LuvFretishe on The Sims Resource.
However, I've noticed that the crib swatches don't change. I attempted to create my own default, but the only file I could find on Skininator was a single baby unisex file: 0A11C0657FBDB54F. Changing the texture with my own didn't change the default skin in the game.

It appears that all baby skins created in the past needed updates after certain patches. Is it safe to assume that editing this object is quite problematic?