During this age range, achild is expanding vocabulary, learning how to communicate more verbally, recognizing themself as a person, and recognizing those around them as persons, not objects. It is interesting to note the toddler is born with a huge number of brain cells, many, many neurons. This is a result of self-preservation, where the brain has had to rely first on frontal lobe thinking, and then, depending upon the situation, reverting to more survivalistic thinking. So, the bottom line is babies are born with many more brain cells than they need, following the philosophy, "it is better to have it and not need it."
As the baby develops into a toddler, and starts acquiring vocabulary and problem solving skills, if new challenges are not presented and mastered by the developing child, those portions of the brain atrophy and are shut down because they are not put to use. To enhance these areas of cognition, language, and social skills, the child should be presented with new learning opportunities. The old saying "strike while the iron is hot" would apply here. The brain is new, fresh, open to all types of different stimulation. The child would get his or her greatest impetus to higher levels of intelligence at these early stages by exposure to different languages, music, social interactions, and other educationally designed scenarios.