There's a cute little column over at 4 Color Rebellion about what happened when an English teacher asked his six year old students about Mario's family.  Strange relationships between Mario, Peach, Bowser, and Wario are presented.  It also seems Luigi is Mario's older brother, as "(h)e's taller".

I'm honestly not sure I find the kids' logic any worse than that expressed whenever the whole "Donkey Kong Lineage" thing comes up.

Go read more at http://www.4colorrebellion.com/archives/2008/02/18/the-genealogy-of-mario-as-explained-to-me-by-japanese-6-year-olds/.