A person is a being, such as a human, that has certain capacities or attributes constituting personhood, which in turn is defined differently by different authors in different disciplines, and by different cultures in different times and places.
In ancient Rome, the word "persona" (Latin) or "prosopon" (πρόσωπον: Greek) originally referred to the masks worn by actors on stage. The various masks represented the various "personae" in the stage play. The concept of a "person" was further developed during the Trinitarian and Christological debates of the first through sixth centuries. Since then, a number of important changes to the word's meaning and use have taken place, and attempts have been made to redefine the word with varying degrees of adoption and influence.
In addition to the question of personhood, of what makes a being count as a person to begin with, there are further questions about personal identity: both about what makes any particular person that particular person instead of another, and about what makes a person at one time the same person as he or she was or will be at another time despite any intervening changes.
The common plural of "person", "people", is often used to refer to an entire nation or ethnic group (as in "a people"), so the plural "persons" is often used in contexts which require precision such as philosophical and legal writing.
Biologically, a child (plural: children) is a human between the stages of birth and puberty. Some biological definitions of a child include the fetus, as being an unborn child. The legal definition of "child" generally refers to a minor, otherwise known as a person younger than the age of majority.
"Child" may also describe a relationship with a parent (such as sons and daughters of any age) or, metaphorically, an authority figure, or signify group membership in a clan, tribe, or religion; it can also signify being strongly affected by a specific time, place, or circumstance, as in "a child of nature" or "a child of the Sixties".