What may be the biggest boost to language-learning ability in children is the extra blood flow and metabolic activity in their brains. Their brains are working twice as hard as adults’. The level of glucose they use rises until age two and then stays twice as high as adults’ until around age nine. Babies’ brains are working in overdrive to make new connections between neurons. It is through those connections that they learn the sounds and words, and then compute the grammar of what we are saying.