I...don't understand. Are you looking for help, or are you looking to get some "kids" to "shut up" and "show some respect for elders"?
If it is the former you should already have gotten what you want -
3DS games work on what is called the '
3DS mode' on the 3DS device, as distinct from "
DS mode" (for
DS games) and "DSi mode" (for DSi games of course, though those can often be played on DS mode just with decreased capabilities). Given that
3DS mode has
not been hacked, i.e.
only Nintendo can access it right now, you cannot play 3DS games on a flashcart, since
no flashcart can access 3DS mode.
Flashcarts
can access DS mode on 3DS, as previously mentioned, and so they
can play DS games on the 3DS, but that's about it. Here is the list of flashcarts which are able to do this:
http://gbatemp.net/t297140-3ds-updates-and-flashcarts-a-faq
If it is the latter than I will only say that that is not the best of ideas. Regardless of how "young" or "immature" or even "smart-mouthed" he is, his opinion is his own, and ridiculing it as stupid, unwise and immature will serve no purpose except to get him defensive (or puzzled, or dismissive of
your own opinions). I don't think you can change his opinions like that, and as you can see it's not effective in getting him to "shut up and listen to you as an elder" either. Or to get him or anyone else to respect you, for that matter.
(Just my 2 cents, for what it's worth.)