I'm actually somewhere between Mostly and Somewhat.
I don't really want them fully mobile like pets/Kittens, but I would like more interactions and some ability to customize them. What I've been saying I'd like is additional items (Bouncy chair, play mat, play pen, maybe a baby bath) that your sim can move the baby between. So it's still tied to items, but you can have several items around the house and move the baby to whichever is closest to where you want your adult sim skilling up. (A baby sling or baby carrier would be cool too, but I think the technical issues to get those to work would be pretty significant.)
And the ability to change the onsie. I'm okay with only having like 4 baby skin tones (including Alien) and no influence on the baby's face. I just would like different onsies.