Frankly, if you're that interested in tracking what your children have and haven't bought, online purchases are likely to be easier, in that they come to your home through the mail.

The general categories of things that children are commonly restricted from buying:

- Drugs. These are all black market, so availability of prepaid cards is unlikely to change how they're bought.

- Alcohol. I've never tried to buy this online; I know eBay Now wanted to sell it and concluded that the cost of legal compliance was too high. Even assuming they could find mail-order booze, it would arrive in the mail, easily detectible.

- Pornography. This can be consumed directly on the computer, raising possible detection issues. However, if you're afraid of children buying it over the internet, I've got some very bad news for you...

- Birth control pills? I'm running out of ideas.

Are you afraid they'll buy digital goods? Why?

> - Birth control pills?

Exactly the kind of thing teenagers should be able to buy without their parents' consent.

You won't find me disagreeing with that, but the fact is birth control pills are controlled.

you need a prescription from a doctor to buy that ;)

> in that they come to your home through the mail.

Says who? Who says they couldn't send a package to a friends house, or a workplace?

If they have a workplace, all hope is lost.

How would you react to receiving a package in the mail for your son's friend?

Oh I know how I would react, but that doesn't mean every parent would react that way.