I have decided to attempt my original intention in this campaign, which was to build the mechanics of the characters behind the scenes using the rules of the Fourth Edition. The children will play their characters with only their notes and sketches. When they want to do something, I will adjudicate it using their powers and statistics and sometimes page 42 from the Dungeon Master’s Guide. This will allow considerable reflavouring of the rules to better match their conceits, and this will prevent the children from becoming distracted by rules and needless details.
Handsword will be an Eladrin Assault Swordmage. This will allow him to "fly" using teleportation, use his sword like a gun with occasional ranged attacks. He will also have the Sidh Lord Theme to allow him to turn his sword into a soldier (summon a fey guard).
Panny will be a Razorclaw Shifter Druid to change into a panda and throw her bamboo spears.
Luna will be a Pixie Bard to fly and to reflect her love of music. Unfortunately the new Character Builder is too awkward and crash-prone to make convenient pdfs, otherwise I would make her a reflavoured Pixie.
Phantom will be an Eladrin Wizard. Once again the children love flying, and teleportation is the easiest way to mechanically represent that at the first level, especially since the boy who is playing this character will not want to play a Pixie.
Sunny will be a Psion: this class seems to fit her anime conceit, and it relies on both Intelligence and Charisma.
Sharon the fox robot girl will use the mechanics of a Drow Monk. We can say that the four hour trance is when she recharges her robotic batteries. She can use the unarmed strike to kick things.
Eberron, and especially Sharn, seems like a good setting for such an eclectic and techno-magical group of characters. Perhaps I shall throw the party together as a band of travelers on the dangerous road, much like in the Canterbury Tales. At any rate before we begin rolling dice, I will use the computer and the beam projector in the classroom to show the children some pictures of Sharn and its various inhabitants and wonders.