Childhood is a stage of life primarily defined by being a student in most developed nations. While the concept has at least three components — legal (i.e., being less than 21 years of age in most states in the US), biological (i.e., being at a stage when most of the body is still developing — until about age 26), and social (i.e., studentdom) — it’s social component is the one by which we think of most children.