Establishing a stable gender identity is seen as a key developmental marker of early childhood. Gender identity usually aligns with the sex characteristics that are used to determine whether a child is registered at birth as either male or a female. By 4 years old, most children will have developed a strong sense of being either a boy or a girl, but in some cases, this identity will not align with their sex characteristics. A rich language, historic and contemporary, has been used to define and explain this. Terms include, but are not limited to, tomboys and sissy-boys, transsexualism, transgender, gender identity disorders, gender dysphoria, gender variance, and more recently trans and non-binary.

Since the 1950s, there has been significant research and debate about the appropriate ...