Seize the opportunity to teach chess and life. Show how adults win graciously, and lose with dignity. Praise carefully planned moves even if inaccurate at first. Teach your child the proper way to point out bad moves. Ugly criticism has no place in chess.
Tournament games begin and end with a respectful handshake.
Two players often meet to analyze their game after the result is posted. The path to victory is paved with many loses. Each lose teaches a lesson. I believe that Chess makes kids smart. My experiences show it to be true.