Biologically, a child (plural: children) is a human being between the stages of birth and puberty. The legal definition of child generally refers to a minor, otherwise known as a person younger than the age of majority.
A man wants no protection when his conduct is strictly right.
William Murray, 1st Earl of Mansfield, Bird v. Gunston (1785), 3 Doug. 275; reported in James William Norton-Kyshe, Dictionary of Legal Quotations (1904), p. 212.