At birth, infants have inborn reflexes, or instincts, such as rooting and sucking reflexes. These reflexes are involuntary responses to environmental stimuli.
From the age of 6 weeks to 4 months, infants gradually begin to gain control over their own bodily actions. This begins at first by accident---with actions such as an infant finding his mouth with his hand and beginning to suck on his fingers. Through the trial and error process the infant will eventually repeat the action until it becomes a habit and can be preformed voluntarily.
In the next stage of development, from 4 months through 9 months, discovery begins again by accident and proceeds through the trial and error process with actions involving external objects in the environment. For example, a child sitting in a bouncy seat kicks her legs, setting off the lights and music on the activity bar. Eventually, through trial and error, the infant learns that kicking will produce the desired action of lighting up the activity bar and playing the music.
From 9 to 12 months, infants begin to develop logical thought patterns by intentionally putting two schemes together to reach a goal or solve a problem. At this stage, new discoveries are no longer accidental but intentional. By putting together two schemes, an infant at this stage, seeing a bowl of cereal behind his cup, will push aside the cup and reach for the cereal. By combining the pushing and reaching schemes or habits, he is able to obtain his goal of getting the bowl of cereal.
At 12 to 18 months, a baby's curiosity about objects in the environment produces explorations in a trial and error manner to make new discoveries. A baby in this stage performs simple experiments to see what will happen or what reactions she will get with different variations of the same activity, such as dropping objects from her highchair.
The stage from 18 to 24 months marks the beginning of creativity and insight. Toddlers in this stage are beginning to form symbolic representations of events, transitioning from the need to have physical representations of objects and events to think through a problem.