I think I've read in the past that scientists theorize/assume that ubiquitous "baby talk" really hinders a kid's vocab/grammar/eloquence development. Makes complete sense. I wouldn't be surprised if the biggest thing the average parent could change that would make a difference in their children's development would simply be to eradicate baby talk and talking down to children completely.
Child development is a really contentious field, which makes sense as people are willing to invest in children (go figure). I've heard this too. Another thing I've read is that the way a baby is carried can affect things as well. What I read mostly discussed whether a baby being held so that its line of sight is over the back of the parent has a different effect than carrying the baby in such a way that it faces forward, can affect how independent a child might become. The article I read (if I'm remembering it right) made the case that a child is initially unable to conceive of itself as a separate entity from its parent until a given stage of development and so carrying the kid in a forward-facing manner will impart it with the idea or impression of greater control, rather than being hauled around like a sack of potatoes. I'm sure someone will come along and argue with that though.