Honestly, the babies in my Sims 2 and 3 games just stay in their cribs anyway. It's good that Sims 3 had the stroller and the baby swing in Generations and the store, but they're mostly a novelty. I didn't really mind the babies being attached to the bassinet, although I'd be alright with having them separated.
That said, I'd like more effort devoted to teens, because the life stage lasts much longer than babies, and there's so much to do for teenagers. I don't mind the height similarity between teens and adults, since at this point they'd have to redo tons of animations from all the packs if they want to adjust teens' heights. I also don't mind teens sharing clothes with adults, because honestly, all the clothes I've had since high school still fit me today. The teens back in TS2 and TS3 also had limited wardrobe choices, while the adults had a lot that could've also worked for teens.
What I would like to see are more teen-specific activities and behaviors. I think Parenthood was a step in the right direction, but that's just scratching the surface. There are a lot of things to help flesh out teens, like proms, skateboarding, sneaking out, etc. I especially liked how teens could sneak out with friends and partners in Sims 2.