this is actually pretty brilliant on eBay's part, since it'll get the kids to only buy on eBay, since thats pretty much the only place where buyers accept paypal(yes others accept paypal too, but on eBay pretty much everyone does).
So it'll generate them fees from sales, and they'll condition the kids to buy their stuff on eBay instead of other sites.
Paypal also has a browser plugin which will generate a one-time Visa card number, for use on sites which don't accept Paypal.
I hear there are some sites on the Internet which take Visa.
This instantly solves a pressing issue for many 13 year olds, namely, how do I pay for my WoW account? And now Ebay will happily take, hmm, about fifty cents of every month's bill. Oh, want to order from Amazon? You can do that, too. iTunes? You can do that, too.
And when you get to 18 and can finally get a real honest-to-God debit card... why bother? You know how to do things via Paypal.
I think this is brilliant. (Note: no financial interest in eBay, aside from moving five figures through Paypal this year.)
So it'll generate them fees from sales, and they'll condition the kids to buy their stuff on eBay instead of other sites.