Ebert really missed the mark on this one
http://rogerebert.suntimes.com/apps/pbcs.dll/article?AID=/20090722/REVIEWS/907229985
"I know I am expected to believe the tenets of a religion on the basis of faith, not common sense, but during this film, I found that very difficult. How reliable are wind directions, the interpretation of ashes and astrological readings? Would you give over your son on such a basis? Would you trust such a chosen one as your spiritual leader?
These matters aside, “Unmistaken Child” has undeniable interest. It is filmed as events occur, in the actual locations, showing a world of great contrasts between an ancient way of life and a society that uses automobiles and helicopters. Baratz doesn’t ask any of the obvious questions, preferring to observe uncritically, and if you can do the same, you may find “Unmistaken Child” worth seeing. I could not, and grew restless."
He assumes that the director and the film are 100% on board with the reincarnation belief. I'm not so sure.
Personally I don't know whether I believe the child is really the incarnation of the lama or not, leaning towards not, but I never felt the movie was trying to coerce me one way or the other. Solid, even handed film imo.
One point for the unbelievers: When they made the child pick "his" former possessions and seemingly got them all right, I noticed that the correct choices were more visually interesting than the incorrect ones. If I was a child I probably would go for the shiny pink beads over the boring brown ones too.
But anyway I think that's really beside the point. It doesn't matter which side you're on, the scene where Tenzin asks the child's parents if they will let him go will destroy you.