In VF1, family members fell in a range between the mother's and father's "heads". In VF2, the kids can come from anywhere in the "heads" spectrum.
VF1 has a basical genetics sytem while VF2 is completely random.
But even if it would follow real-life genetics system, it'd still be pretty possible to a blondie pop up from brunette parents. You'll probably learn more about it at school within biology class or whatever it's called at where you live
BTW i prefer VF2 one because you have chance to accumulato much more variety of head types. And also it has really beautiful hair colors that don't naturally exist in real life