"The Smurfs' Village," a game for the iPhone and other Apple gadgets, was released a month ago and quickly became the highest-grossing application in the iTunes store. Yet it's free to download.So where does the money come from? Kelly Rummelhart of Gridley, Calif., has part of the answer. Her 4-year-old son was using her iPad to play the game and racked up $66.88 in charges on her credit card without knowing what he was doing.