Haha. The 13 year old girl with her menarche most probably heard about it from her friends. Her parents don't really need to educate her.
As for the notion of the mother and father, everyone has biological parents (they do have a parent of each sex, whether it be through artificial insemination etc), but people they grow up with may pertain to an assortment of sexual orientations. I think the most important role parents and guardians can play in a child's life is to mentally nurture, support and provide for them. This takes patience and understanding, and is not necessarily limited nor inherent to any gender.
I think the argument that males and females perform according to a certain function (with respect to a child's upbringing) is somewhat outdated. The social construct that females are nurturing figures and that males are breadwinners is growing thin. The pressures are still there but the distinct roles have merged.
My mum won't necessarily be the one to teach me how to sew or cook, nor will my dad on how to change the car's engine oil and filter and soldering components of an electronic circuit.
This is what DIY books are for.