The boy has metal caps on some of his teeth, much like Jack does. The only difference is, his are blackened and clearly not made of gold unlike jacks :D
and another thing, When the crew in the Chinese ship (captained by Barbossa) is sailing to retrieve Jack, there is a shot of the water reflecting the stars. The reflections do not match up to the stars above...
There is a list of more "goofs" as they are called posted on imdb.com...
