Terminal Command to Create Folder for Every User

Here is what I tried: sudo -> password mkdir /Users/*/Sites However, three accounts already have /Sites, so I got an error saying /Sites folder exists in such and such account. However, it didn't make /Sites in the other 100 or so folders. I run the Xserve as classroom Webserver hosting student sites. I created user accounts using Webmin and the directories are empty. For student Websites to show on the Internet, they have to be in their /Sites. So, I need a way to create /Sites for every user, excluding those accounts that already have /Sites.