This reminds me so much of the Simpsons episode with Homer's long lost brother, Herb (he invents a machine to translate baby talk). I think, from my own experi

This reminds me so much of the Simpsons episode with Homer's long lost brother, Herb (he invents a machine to translate baby talk). I think, from my own experience, babies learn to communicate in a two way fashion - they try noises and responses with their caregivers, and when the caregivers respond in an agreeable fashion, the baby stores that bit of communication away to try again later (and possibly reinforce). So I think some of their communication is learned (signals for positive/negative), and quite specific to the baby-parent pair, while some will be instinctual (e.g. I imagine the excited kicking to be related to an adrenal surge or something, and early-infant crying is definitely an instinctual distress signal)