I personally know a person who went to the hospital from a caffeine overdose. She was a thin person, in graduate school and so focused on getting ready for exams. She just drank coffee after coffee after coffee. It affected her heart-rate and made her 'out of it'. She stayed in the hospital overnight and it took her a couple days to recover from the stress. I think her small size and not eating (just drinking coffee continuously) had a lot to do with her overdose. So I can see how someone small, like a kid, with an underlying heart problem, could actually die.