Kohlberg (1966) theory of gender consistency
Gender Identity- The child is aware that they they're male or female, but think their gender might change (e.g. by wearing opposite sex clothes). The stage usually occurs between the ages of 2 and 3½ years old.
Gender Stability- The child realises that their gender will remain fixed over time (e.g.boys will become men). However, they may think that gender can change in different situations (e.g. when doing an 'opposite sex activity'). This stage usually occurs between the ages of 3½ and 4½.
Gender Consistency- The child is aware that gender remains fixed in different situation (e.g. cross dressing doesn't change gender). This usually occurs between theages of 4½ and 7.