This is a question that, as you might imagine, has been on my mind lately. Fortunately, this excellent TED talk by Alison Gopnik has largely answered the question for me. In short, babies are for learning–and by learning, she means what we call playing, or "getting into everything." This seems a very important point, given the way playtime is under attack in our culture, not only in school programs but in general (don't even get me started on the whole Leapfrog thing). Points covered in this talk include
– How babies are smarter than you.
– How childhood makes you not a chicken.
– Why, when we say young children "can't pay attention," what we really mean is that young children can't not pay attention.
– What being a baby is like ("being in love, in Paris, for the first time, after three double espressos").
I can't figure out how to embed the video easily, but you can watch it here: http://www.ted.com/talks/alison_gopnik_what_do_babies_think.html
The Procrastination Salon 
Thanks, lady, for posting this. Of course, my child-raising days are in the past and my grandchildren are entering puberty, but I have saved the talk, because I know people who are facing the challenged addressed.
My Inner Cynic recalls the episode of “As Time Goes By” where Lionel and Jean go to a party hosted by Allister and meet a girl who is anguished over the question “Should one breed in such an uncertain world?”