For a start, I never realised that Microsoft offer "child" account for their users who are 12 and under, and a "teen" account for 13-17 year olds. The still need their parents credit card though! This is an interesting contrast to a Google Account, where you are completely out of luck if you are under 13.
Parents can also set the highest ESRB rating that these accounts can download, and purchases can be blocked completely if required.
Worth checking out the post if this applies to you (thumbnail image by Andrew Stawaz, Flickr).