For the first two years of a baby's life, they're taking in a lot and not putting much (besides dirty diapers) back out there.  We actually train our babies like a dog for the first two years.  "Watch this trick... say 'dadda'".  Sound familiar?

When you see a baby walking, crawling, talking or laughing, they're doing what they've been trained to do, not because it makes sense to them quite yet.  You could carry on a lengthy conversation with a baby and never get anywhere... much like a conversation with a radio DJ.