2) Trading could be done on here or on sites that accept bitcoin
3) The most important thing to teenagers: videogames
4) I might be an exception but I now exactly what silk road is and I have never even been on that site.
I think that bitcoin has thought me a lot of things including stuff like forex trading or negotiating with potential clients (check my trust for more info).
Source: My own experience of the Bitcoin Market.
I also forgot that not every kid is a bad kid and will find Silk Road, but its definitely there. I did a quick search and found MANY sites offering video games for Bitcoins so it could work out very well in fact. I just dont know if kids would want to jump through the hoops of figuring out Bitcoin, but it shouldn't be an issue as their parents are going through the hoops getting it for them. Some parents might also not like how there is no way to identify who their kids are paying.
Nice. My youngest (still at home) gets the equivalent of $20 a week in Bitcoins sent to an Electrum wallet. I let her cash out to me if she wants to buy something or spend them on her own if she wants to. She bought a few things on Amazon back when SpendBitcoins still serviced the US market but since then she has become a hoarder. lol
She keeps telling me that she's going to be rich someday from her allowance. They really grow up too fast (and listen to dad a little too much I think).