The brain grows dramatically through the second year of life. Around 12 months, toddlers develop a new ability to remember experiences that occurred a few hours or even a day earlier. Toddlers often demonstrate this new ability by repeating a recalled experience, such as throwing a ball or stacking blocks, at a later time. Changes in the brain allow a toddler between 18 and 24 months of age to think in more complex ways, such as recalling events that occurred days earlier. The older toddler begins playing pretend. For example, he or she may give a teddy bear a "drink" from a cup or let the bear "talk" on the phone. These toddlers are also beginning to understand symbols (for example, that words can stand for objects).
Toddlers also begin to see connections between events. For example, when they open a music box, they know they will hear a song. Or when they throw a ball, they know it will bounce. They'll probably throw their dolls, food, and many other objects to see if they'll bounce too.
At 18 months, toddlers have developed a greater understanding of the world outside of home. Toddlers begin to develop a sense of self, the ability to see themselves as separate from others. They can now imagine a threat and often go through a period of clinging to parents and being fearful of strangers.