As a parent, I know the aggrivation of the kids getting out cup after cup, not keeping up with it, and before too long, you have no idea which cup belongs to which child. This is especially annoying when you are a blind parent and can not rely on colors to differenciate the cups.
Here's a product that can help with this and a host of other labeling issues in the kitchen.
Bumpy Name labels are elastic rubber "orbit" labels that come in sizes to fit a variety of containers.
They're dishwasher-safe and can be made in print or Braille, and you can order custom labels with a second line of information, such as "No Dairy," or the child's phone number. They are available at http://www.bumpyname.com in either a package of three stock names or a package of four custom labels. Get a bunch of these and just go crazy labeling stuff!