An interesting question we often receive from parents is at what age should they begin training a childs vertical leap. It is a tricky question an there is no clear cut answers, but we will try to give some pointers to help you decide here.
A childs body is fragile, and therefore should not be pushed to extreme limits while they are too young. You do not want to start putting your kid through extreme vertical jump workouts or weight lifting routines at a young age. It can be overly hard to their body, stunt growth, and cause problems in the future for them. But then the question becomes what age is considered to young. Well in the case of males, you want to atleast wait until they have gone through puberty to begin any sort of intense training.
If your child is going through puberty or has yet to hit that stage, and you want them to do some sort of workouts or exercises make sure to proceed with extreme caution. Stick to simple things such as bodyweight movements like nonweighted squats, lunges, calf raises, pushups, pullups, and things like that. Balance and coordination are great things to be taught at this age, so it would probably just as effective, if not more effective to spend your time on that rather than strength. At this age, it will be for the most part worthless to put them through a full training routine, so if you decide to just focus on building up simple strength, balance, and coordination.
When your child has gone through puberty, it may then be reasonable to begin putting them through light weighted exercises or simple plyometric routines. DO NOT jump in to fast. If you are starting at this age there is plenty of time for them to build up to higher amounts and larger levels of intensity. Keep it simple. There is no reason to push them too hard. This should be during or towards the end of middle school, around the age of 14-15.
By the time a child is entering high school, and is around 15 to 16 years old, is when it is appropriate to begin taking the training to the next level. Hopefully you have worked them into it properly so that it will not be a shock to their system. By the time they are 17 years or older it can in most instances be assumed that their physical maturity is nearing adult form, and therefore they can begin full vertical jump programs and weight lifting routines. If you have been slowly working them into these types of routines, then they will have already developed nicely as a youth athlete and be ready to maximize their potential and reach their prime in their last few years of high school.