M. Night Shyamalan has a go at an old-fashioned Saturday-matinee children’s film, a live-action adaptation of the Nickelodeon cartoon series about the boy avatar who alone has the power, if he can learn to master it, to command all the elements of the four rival realms of Air, Water, Earth, and Fire, and thus to enforce peace between them. The writer-director, no surprises up his sleeve, infuses it with a commendable fairy-tale earnestness, so that even the naïveté has its charm (“It is time to show the Fire Nation that we believe in our beliefs as much as they believe in theirs”), and the creatures, the ships, the other special effects are more than acceptable, yet the whole thing feels somehow remote and uncompelling. And the after-the-fact conversion to 3-D is useless. With Noah Ringer, Jackson Rathbone, Nicola Peltz, and Dev Patel. (2010) — Duncan Shepherd