Chicagoan (well, Wilmettian) Julia Sweeney describes doing "the talk" for her kid. It turns out that even being a professional sayer-of-embarrassing-things—remember Pat?—doesn’t really prepare you for telling your offspring how they came to be.
(My only real memory of sex ed: in middle school, my English teacher had a farm, which we went to every week. One day, a classmate picked up a small farm instrument that looked like a medieval torture device, and asked what it was. It was an elastrator, which places the rubber band that turns a bull into a steer. Thus, with wide eyes, began our alternative-school sex ed class. Reader, it worked! Parents, if you want your kids to practice abstinence, forget the abstinence-only classes, put down the condom and the banana, and kick off your child’s education with an elastrator. You may want to hold off on chicken sex, though; you don’t want them to be haunted. I’m waiting for federal funding for my animal-husbandry-only curriculum.)
Sweeney gives her talk a much longer treatment in the Guardian: "people figure the legs out. They just do."