Running fast depends on several factors:
1) Reaction time (moving quickly based on a stimulus)
2) Acceleration (changing speed quickly)
3) Max velocity (reaching a high speed)
4) Overcoming deceleration (maintain speed without slowing down).
At its most basic, kids just need to learn to move fast. This can be done by creating games or situations where they race. Some games that work great are cat and mouse chase games, tag, and throw a ball in front of you/sprinting to catch it before it bounces twice.
Outside of track, other field sports are multidirectional, meaning the distances and directions can change. This is heavily seen in Football, Tennis, and Basketball, to name a few. To practice this, we can modify these drills (or races) to be done linearly, running in a curved pattern, or adding a change of direction prior to the all out sprint. You can add obstacles or add in components like dribbling a ball or carrying an object.
To add novelty to the reaction time, change the starting stimulus. All of these games or races can start statically (from a dead stop) or dynamically (from a moving start). For example, start the race on a verbal command or visual command (these can be changed). Also, vary the static starting stance to the race or game. For example: lay on your stomach, back, or side, start seated or start on one knee, start in a push up position, or start in a sport stance. All of these can be started dynamically: backpedal, skip, forward roll, cartwheel, and shuffle.
These methods can be mixed and matched together in endless combinations to help kids improve their speed, agility, coordination, and fitness. For youth athletes, this novelty can help make the training more engaging and fun, resulting in more consistent and overall better athletes.