If I were you, I would teach that kid how to filter information on the internet. I would teach him that you shouldn't depend only on one source and you have to check the same information on multiple websites, including forums too.
Well said, OP doesn't need to explain or try to convince that kid about bitcoin or fiat. Instead, teach him how to filter information and provide reliable sources of information. That way, he will be able to find out the truth about bitcoin himself and have the most correct and realistic view of bitcoin.
Don't waste time explaining and convincing him or anyone, because that will make us look like we need them or are trying to trick them. There is no better explanation or persuasion than letting them find out the evidence, the truth, for themselves.
Yea that's it. The goal right now is not to convince anyone to invest in bitcoin or adopt it. Rather, to understand Bitcoin from different viewpoints and sources. That kid has only read the negative half-baked information from the internet, it is our duty to direct him to other places he can get genuine information; not neccessarily a place where he will get overhyped information about Bitcoin.
If possible, refer this forum to him so he can get authentic information. The choice should be his to make at the end if he wants to hold on to the initial information he got or be open to learning.