Well aside from the whole parent/bank acct thing, I am going to address the original question--how to buy.....
Get some cash, go to Eckards, Walgreens, Radio shack, Rite Aid --- get yourself a prepaid credit card--you give them cash, they give you a visa or MC.
Then you can just go to amazon and buy them......
They don't send a statement since it is prepaid so you are good to go.