And when I say children, I mean at or under 13. Have you ever tried it? Do you have any references, quotes, or guidelines that you live by in the effort? When I think of children, I think of slightly simpler adults. Smaller vocabulary, less articulate, but otherwise mostly the same; after all, kids emulate adults because they think we're cool. No matter how dreamy or carefree the child, in all likelihood there's a version of that some fifteen years older which can be used to inspire the character.
When writing as children, I try to see the world as open minded as I can. (depending on how the kid was raised) I don't make them stupid, but I do tend to write them with a more curious vernacular. Unafraid to ask questions, and at the same time feeling like they know enough (At least against adults) I also let things affect them more. Make them question themselves or whatever just happened. Because like I said, they're curious.