Right now (Saturday morning) there are two bestellers in Amazon’s top 100 Children’s books that are Kindle editions, i.e., for its digital e-book. There are none in the Top 100 for adults. Does that mean more Kindle users are kids? Doubtful. The more likely answer is that more Kindle users are nerds. The two Kindle titles are both fantasy bestsellers: Christopher Paolini’s Brisingr (no. 8 in kids’ and no. 1 as print) and Neil Gaiman’s The Graveyard Book (no. 34 and no. 9).
There are no Kindle editions in this morning’s Top 100 in Amazon’s SF & Fantasy category, but it looks like paperbacks drive that list, pushing hardcover and digital editions down from higher rankings.