Before this week I hadn't really introduced the girls to skip counting or really into counting much above 20. They could do it a little (just counting, not skip counting), but I had never stressed it. We had some nice weather though, so while we were playing, I wrote the numbers 0-100 by tens on the sidewalk. Then I had the girls skip as they counted them. They were doing pretty good remembering what each number was too.
It was a simple way to practice their counting, and they thought it was a pretty fun game.