Babies are born with billions of brain cells. During the first years of life, they form connections with other brain cells. Over time, the connections we use on a regular basis become stronger.
Those cells we do not use, die off. This is the time when children are open to all forms of language. Early experiences contribute significantly to the structure of the brain and its capacities. The quality, quantity and consistency of stimulation will determine to a large extent the number of brain synapses that are formed and how those connections will function. This is true for both cognitive and emotional development, and the effect is life-long.