Answer:
Gender roles
Step-by-step explanation:
In psychology, the term gender role/sex role refers to the range of behaviors and attitudes that society considers as appropriate for people based on their biological sex. In other words, it's the roles that people consider appropriate and desired for "boys" and "girls"
In this example, the act of encouraging young girls to wear dresses while encouraging young boys to engage in contact sports is a way of sending the message that it is appropriate for girls to wear dresses while it's appropriate for boys to engage in contact sports. Therefore this would be an example of gender roles or sex roles.