Open 24/7
When my oldest daughter was about 5, while driving along, we saw a sign on a grocery store that said, "Open 24 hours a day, 7 days a week" (this was long before the shorthand "24/7" was in use).
She thought about it a bit, and said, "Well of course if they were open 24 hours a day, it would have to be 7 days a week. Otherwise, they would have to open and close at midnight."
That's when I knew I had a chip off the ol' block!