Have a look at this great and very entertaining talk of Alison Gopnik on "What do babies think?"
"Babies and young children are like the R&D division of the human species," says psychologist Alison Gopnik. Her research explores the sophisticated intelligence-gathering and decision-making that babies are really doing when they play.
Alison Gopnik: What do babies think? | Video on TED.com
If you want to learn more about Alison Gopnik's reasearch, you might want to read her article: Your Baby Is Smarter Than You Think or her book The Philosophical Baby: What Children's Minds Tell Us about Truth, Love and the Meaning of Life.