All these years and I didn't know you could stick a baby in the inventory. Doh! *slaps forehead, cackles and twirls evil mustache*
But seriously. I agree with your points on interaction and providing better cribs. Sims 2 had a decent selection of baby furniture and toys, 4 feels very rushed, similar to toddlers when they were first added.
What I most disliked is that as soon as my Sim left the room after feeding/giving them attention, they started crying, and have since used a mod to rectify this problem. However, the guessing game and babies in general has never really bothered me. Likely because there's much more important stuff I still want to see worked on first. Toddlers, imo, are a step worse as far as neediness goes. Personally, I think they could use more animations (i.e. drooling, gurgling noises, happy squeals, etc.) and perhaps a few different preset body sizes (there are chubby babies, lol), but that would probably require them to not be an object. Yeah, it's up in the air. Honestly, I don't expect much else from a baby, it's fairly realistic in the 'eating, sleeping, pooping' department.
On a lighter note and given this is the Sims franchise we're talking about, let's hope they don't overdo it in the future, causing them to turn out like Jack Jack...