The rocket's heading once the rocket engages is a huge challenge. There's all kinds of random collision forces applied to it on launch, it's almost sure not to be pointed at the zenith once it escapes the launcher. When combined with the randomness of the rocket's engage time, it's essentially like launching an explosive in a random direction a few dozen feet above the surface.
However, I encourage him to play with rockets anyway. Maybe he'll try to slingshot a rocket into the upper atmosphere someday. Maybe he'll develop a system to slingshot things into low-earth orbit. He might be the savior of the space program with this technology. We can only hope.