Kidshealth.org has some good materials exploring sportsmanship ideas with different age youth. Start with a discussion such as:
Describe what it means to be a good sport.
Follow-up with one of the age-appropriate activities found here: http://kidshealth.org/classroom/
Activities include such things as deciding if a player in the case example is behaving as a good sport or not, make a skit about sportsmanship, etc.
Source: Kidshealth.org
CRE Calendar Usage: 2nd Edition