Sports should be fun for kids, the second you take away the fun, so does the interest in that sport. It doesn't matter what sport you practice for, there should be time set aside for some fun activities. Most often a coach can achieve his/her objectives even with some games implemented within his training program. For example, if you need your athletes to workout aerobically, or elevate their heart rate for 25 minutes, instead of having them jog for 25 minutes, just have them play some soccer game for 25 minutes. If you want to get some short burst speed workout, have them play some tag games, or who can sprint the fastest 30 meters. There will always be ways to make sport fun for kids, this will keep them motivated and active.