SGPL Teens

I was listening to an older podcast, and they brought up a good point about children's literature, how there are so many science fiction stories for children, but they aren't recognized. For instance, Gary's grandchild has a favorite series thats about baseball cards. In the stories, this child collects the baseball cards and if he holds them by his heart as he's sleeping he will wake up in the world of whoever was on the baseball card. That is a time travel story. Time travel is science fiction. Yet, this wouldn't be recognized in a children's section of a store or library. It would likely just be categorized under "Series". I think that is wrong. For any child who wishes to read sci-fi, it is made very difficult for them to find the genre. Fantasy, however, is a huge genre for children. Most children's books are fantasty: The Wizard of Oz, The Hobbit, The Indian In The Cupboard, Trumpet of the Swan, The Chronicles of Narnia, Inkheart, Winnie the Pooh, The Graveyard Book, Harry Potter, etc. But you don't find any sci-fi for children in such mass like you do fantasy. The most namable children's sci-fi would be Tron, The City of Ember, The People of Sparks, and Ender's Game (and other Ender Novels, not all of which are children's). Honestly, I can't think of anything else. Of course, it is an entirely different story for Young Adults/Teens as here we start to get more science-fiction, but still not in mass amounts until you get to the adults. So, why do we not have science-fiction for children. Is it because they wouldn't understand it? I doubt this. Most kids nowadays know computers better than I do, and I've been using them since I was about 7. The children love the Ender Books. So why do author's not write more children's science-fiction? The only thing I can think of is that it would be very difficult to "tone it down". Most science fiction has quite a bit of adult themes, sex, drugs, etc. Because most of science-fiction is set in the future and we can't picture a "nice" future. We, as humans, know that the way we live now is guaranteeing us a gruesome future with less government control and more anarchy, more freedom. Who can control a space ship that they can't find on a radar? If you can jump through black holes and end up in another dimension completely, no government can really have control over you. And because of that mixed with our basic human instincts of pleasure, most science-fiction is rough around the edges and dark. Not pleasant for children. So writing a science-fiction story that is less dark and more "G-rated" would be quite the task. If you have any other ideas why there isn't science-fiction for children, or even if you want to argue that there is, feel free to comment. I'm very interested in hearing your thoughts about this. Here is a list of other YA science-fiction. Some of it would be suitable to older/more mature children as well.