Again, I agree in part. With young athletes, max effort sprints as part of training program are going to produce positive results. However, as you will read in either Mike Boyle or Eric Cressey's articles, getting stronger and more explosive is a must, if you want your child to reach full potential. Incorporating bilateral and unilateral squats, deadlifts, plyometrics, etc. are going to provide the most bang for the buck IMO. The weight needs to be appropriate and in cases of younger athletes with limited training experience, body weight exercises are a great place to start. However, there should be a progression once they master movements using their own weight.
As Dominik pointed out, sprints need to be performed with max effort and appropriate rest between each sprint or you are conditioning the athlete instead of developing speed. I would start out with a 12:1 rest to work ratio as EC recommends. Make sure you monitor athlete closely. Once you recognize fatigue or times slowing significantly, end the session.
Another good recommendation is to always work on speed development prior to strength/power training. Final recommendation is to find a performance coach who is knowledgeable in regards to strength, speed, and agility training and has a great reputation. They do this for a living!
https://ericcressey.com/the-5-...ty-coaching-mistakes
Couple of paragraphs from Mike Boyle:
"The problem is fast feet don’t use the ground well to produce force. Fast feet might be good on hot coals, but not on hard ground. Think of the ground as the well from which we draw speed. It is not how fast the feet move, but rather how much force goes into the ground. This is basic action-reaction physics. Force into the ground equals forward motion. This is why the athletes with the best vertical jumps are most often the fastest. It comes down to force production.
Often coaches will argue the vertical vs. horizontal argument and say the vertical jump doesn’t correspond to horizontal speed, but years of data from the NFL Combine begs to differ. Force into the ground is force into the ground. In spite of what Brett Contreras may say, vectors don’t seem to matter here. The truth is parents should be asking about vertical jump improvement, not about fast feet. My standard line is “Michael Flatley has fast feet, but he doesn’t really go
anywhere. If you move your feet fast and don’t go anywhere, does it matter? It’s the old “tree falling in the woods” thing.
The best solution to slow feet is to get stronger legs. Feet don’t matter. Legs matter. Think about it this way: If you stand at the starting line and take a quick first step but fail to push with the back leg, you don’t go anywhere. The reality is that a quick first step is actually the result of a powerful first push. We should change the buzzwords and start to say “that kid has a great first push.” Lower body strength is the real cure for slow feet and the real key to speed and to agility. The essence of developing quick feet lies in single-leg strength and single-leg stability work… landing skills. If you cannot decelerate, you cannot accelerate, at least not more than once."