Child
A child may be defined as someone who is either below the age of majority/age of consent (minor) or a prepubescent. Familial usage (regardless of age) is not an issue of relevance to intergenerational sex.
Childhood and by extension, the status of human beings as children is an unstable concept. It has been suggested by some historians such as Aries that the concept of childhood is itself an invention of the second millennium.
Childhood innocence and vulnerability
Central to the issue of intergenerational sexuality is the concept of childhood (sexual) innocence and its postpuritanical/utilitarian counterpart, vulnerability.