Clarify the term fair discrimination and explain why employers often employ young females instead of young males

I think that discrimination is always unfair but in some cases is allowed by law or certain standards in some countries and when that happens it is called fair discrimination. Employers often employ young females instead of young males because in general they think that young women are more responsible than young men.  

to get a better life and have children that they get to see grow up better than they did.