Do we have to use EVERY glass in the house by the end of the day???
I only have two kids, and they would go through about 12 glasses a day. They would take one out, fill it, drink half, leave it on the counter, and forget which one was which. God forbid they drink out of the other one's glass, so next time they were thirsty...just grab another glass.
These markers are free and so easy. Cut an old t-shirt into quarter inch strips (I used a rotary cutter, but scissors work just as well). Thread the strips through the button holes. If you need help, use a paper clip. Put it around the glass, pull as tightly as you can, tie in a knot, and cut off the extra. For the ones above, I used two buttons on each to make them a little more interesting.
We use Ball jars for everything...dry storage, leftovers, and drinking glasses. These are wide mouth pint size jars. At about $10-$15 a case, Ball jars are very inexpensive, easily replaced, much sturdier than most glasses, and just fun.
If you don't have a button collection, try starting one. You can usually find containers of them at yard sales and thrift stores. They are great for little home projects and crafts for the kids.
Have fun!