As with any exercise program, the best one is the one that you can realistically keep up with over an extended period of time. Training programs for competitive skaters are very rigorous. In preparation for competitions the skater must improve their anaerobic endurance, since the skater's heart rate is way above what they could maintain for any length of time. For the rest of us, aerobics classes are a good bet. Find one with lots of floor work and stretching.
Stair climbing is excellent.
Try taking them two at a time. Weight training is also good, especially for improving jumps. But weight training is not for kids because of the potential for long term damage of a growing skeleto- muscular system. In skill sports, such as skating, there are two schools of thought here. This supposedly will prevent psychological and neuromuscular confusion over whether you're performing the desired skill, or the weight activity that's like it.