This may have been posted somewhere already but... on the M Night fans website there are photos of a kid (possibly) set to play a young Aang. Thinking Noah Ringer looks like an older version of him? Here is the link: www.mnightfans.com/avatar/. No source, though, so still speculative at this point.
"Do you remember the 21st night of September? Love was changing the minds of pretenders, while chasing the clouds away."