I have a nephew that did something similar to this. He used his mom's CC to purchase credits for some crappy facebook game. He would take $10 or so at a time hoping that his mom would never catch on. His mom isn't computer savvy at all so he was able to pull it off for a few months. Once she discovered it, i looked into it and found that the purchases being made online were coming right from their own IP address.
He was ground for a few weeks.
The kid was 13.
Do you give your kid an allowance? Personally, i thought if his parents gave him a weekly or bi weekly allowance, then he wouldn't feel a need to steal.