It covers at least two major areas: anthropology (common or accepted practices across different cultures), and informational (background which is useful to individuals who may be engaged in, or considering, sexual activity)
Those which tend to emphasize innate biology, which may be encouraged or disturbed during childhood. That is, that human sexual development is primarily a biological process and thus basically similar across cultures, and that there is thus a relatively narrow model for healthy sexual development, although this may be disturbed by the influence of the larger culture or by other means. This is the approach used most often in the medical study of child development.
Those which tend to emphasize sexuality as a social construct (with child sexuality strongly influenced by the larger society). This latter school often uses the terms normative (culturally appropriate behavior) and non-normative (culturally inappropriate behavior),and is the approach used in most social scholarship and most discussed in this article.
Freuds 1905 work Three Essays on the Theory of Sexuality outlined a theory of psychosexual development with five distinct phases: the oral stage (0 - 1.5 years), the anal stage (1.5 - 3.5 years), the phallic stage (3.5 - 6 years) culminating in the resolution of the Oedipus conflict followed by a period of sexual latency (6 years to puberty) and the genital, or adult, stage. Freuds basic thesis was that childrens early sexuality is polymorphous and that strong incestual drives develop, and the child must harness or sublimate these to develop a healthy adult sexuality.
Freud hoped to prove that his model was universally valid and thus turned to ancient mythology and contemporary ethnography for comparative material.