What I find amazing is that kids have an innate sense of pacing. That's not to say we don't need to adjust it during the revision process, but they understand that if you're writing an action story, you don't bog it down with a lot of description of setting and emotion. This story moves at a clip!
The reader doesn't know what the brothers look like, but we definitely know their personalities. They're funny and sarcastic ("Shut up, Adam!" exclaimed Michael. "You sound like a grown cat being forced to take a bath!") and they're ready to fight for each other and their allies. Readers don't need to have the rocket ship described if the characters inside it are painted vividly . . . the ship is just a vehicle. Even in space, good characters drive a story.
Image by NASA (http://adc.gsfc.nasa.gov/adc/images/nasa-logo.gif) [Public domain], via Wikimedia Commons