found that children under the age of four, who showed no signs of gender stability or constancy, nevertheless demonstrated strongly sex-typed behaviours and attitudes
Kohlberg - constancy is required before gender roles
Zosuls (09) observed children playing and concluded that they were using gender labels by 19 months. However, they may show gender typed behaviour preferences earlier than this.
showed 5 and 6 year old children pictures of people carrying out activities. Sometimes these pictures were schema-consistent (for example, a girl playing with a doll) and sometimes they were gender-inconsistent (for example, a girl playing with a gun)
recall for schema-consistent pictures was generally good. However, when schema inconsistent pictures were recalled they were often distorted so that the expected sex was remembered as carrying out the activity (for example, children recalled that the boy had been playing with a gun rather the girl)
This theory can account for why children's beliefs and attitudes about sex roles are so rigid.
Children ignore behaviours which go against gender schemas, e.g. female mechanics
Studies support this, e.g. when young children watch films which depict contradicting gender role behaviours, they tune them out