In 1978, the very first feature-length Superman Movie was released and is still widely accepted as the best film-version of the Superman franchise.  The film had a primarily lighter tone but could, occasionally, border on very serious, mature themes such as the scene where Lois Lane temporarily dies.  The film still holds up to this day minus a few scenes.  But, no one scene feels more out of place and more odd then the 'child getting slapped' scene.
 
At about the middle of the film, Superman shows himself to the world after saving Lois Lane from a falling helicopter.  After this scene, Superman, feeling an adrenaline rush from the rescue, continues to do good things around Metropolis throughout the night.  He does incredible things such as stopping criminals from getting away with crimes and so on.  It's all very heroic and cool to watch because, up to this point, we, the audience, hadn't seen Superman act like a superhero.  The night of being a superhero ends with Superman saving a cat that is stuck in a tree at the behest of a little girl.  This scene was put in to show that Superman will help everyone with every problem no matter how big or small that problem is.  There's nothing wrong with that.  What's wrong with this scene is...well, just watch;