I believe that only antidepressants effect the serotonin level. The stimulant meds do not.
I don't think that you will find a study that looks at high caffeine levels in a child because the only way to do that is to caffeineate them which would be unethical. If a child is loaded up on caffeine, I could understand why there would be problems.
so i am not really sure where you are going with this question? I can tell you that high caffeine levels in a child is not good.
Im excited about the possible response to this!