It is a human being between the stages of birth and puberty, or between the developmental period of infancy and puberty. It may also refer to an unborn human being.

For the UNICEF Convention, a child means every human being below the age of eighteen years unless under the law applicable to the child, the majority is attained earlier.

In the context of urban systems, the Child is a phase that a human being goes through. The following subphases are covered: Early childhood (birth to age 5), middle childhood (ages 6 to 12).