That would require some time travel considering that The Sixth Sense came out months after The Phantom Menace and was filmed over a year later.
Talk about an anachronistic fail on my part. You're absolutely right. I was working at a video store at the time and I do remember having many conversations with customers at the time about that having been a possibility, but of course this was well after the release of both films and I just remember feeling like Lucas had lost an opportunity. But whether Osment would have been ready the full year and a half before release, or whether he had even been known is quite debatable as you point out.
I still stand by my opinion, however, that Osment would have been a much better casting choice.