If you want to be a successful runner, you have to consider everything. It's no good just thinking about endurance and not to develop fine speed.
~ Arthur Lydiard
Athletes need to enjoy their training. They don't enjoy going down to the track with a coach making them do repetitions until they're exhausted. From enjoyment comes the will to win.
Encourage kids to enjoy running and play in athletics. Don't force them to run too much competition.
Train, don't strain.