Commence with getting them involved in team sports or dance teams. With me during my formative years (4-16) I was involved in team sports. We learned to sacrifice self-interests for greater team goals and most significantly we learned that working as a team as 1 unit we could create a synergy that would jettison us above and beyond with regards to achievement and awards. This attitude has followed me throughout life.
Our children became involved in Irish Step Dancing when they were 4. Irish Step Dancing has both individual and group competition. Yet most of your time and energy is devoted to practice, practice, practice for both competitions and group shows. Thus one (once again) learns to sacrifice self-interest for team goals such as timing and filling show-niches based on your strengths and weaknesses.