Catherine asked to do numbers, so I gave her a sheet of 1's and 2's:
Catherine knew all the letters, of course. But I think it was a helpful exercise for her too because she had to scan the page for a particular letters, which is great practice for reading. I also loved her innate work efficiency: she picked up the first color, marked all of those letters, and then moved on to the next color. On some later sheets, I wrote in some extra letters which were not the target letters to trick her. She immediately noticed the extra letters and pointed them out to me.
For both it was also a good lesson on reading a legend for information, but we actually called it a "chart."
Another great advantage to this activity is that it kept the girls busy long enough for me to clean the kitchen!