To rescue yourself from your own impatience (and the clutches of the diet industry that feeds on it), you need to moderate your thinking.
The total daily calories your child consumes should be enough to support a normal rate of growth and development for his age group, in addition to meeting his energy needs.
Medicine balls are a great way to exercise any area of your body, whether upper, lower, or core. There are different sized exercise balls from 2-12, that you can use for numerous different exercises.
Many people want not just strength, but to build lean muscle, whether as 'bulk' around an already lean frame, or to lean out overall. There are few key principles that you need to abide by if you want success.