Leo is 3 years old. He knows he is a boy but thinks that if he puts on a dress, he will become a girl.

His older sister, Maya, who is 5, actively avoids playing with toy trucks because she says they are "for boys" and only plays with dolls, which she says are "for girls". When shown a picture of a male nurse, Maya later remembers the person as a female nurse.

Discuss cognitive explanations of gender development. Refer to the cases of Leo and Maya in your answer.