In 2004, I got my first period on my ninth birthday. My 12-year-old sister had just gotten hers one month before (apparently, one sister getting hers can 'trigger' the other if they are close in age). My mom had gone out to get my birthday cake when I started screaming in the bathroom, so my sister had to explain the whole thing to me. On my birthday! With a troupe of fourth-graders coming to my party in an hour! My sister's explanation that "every month a little man comes to sweep out your insides to keep a room ready for a baby" was... not accurate. It did not help my panic. If she'd been told the truth, or if I had, I wouldn't have freaked out and thought I was dying! My kids are going to know what periods are when they're 5/6. Whenever they're ready to ask where a baby comes from, they'll get the run down. Because there's nothing shameful about biology, and no reason to scare the shit out of them for bleeding randomly one day while they're waiting for their Spongebob Squarepants birthday cake.