Earth: flat and round

Out of the blue Sparkle asked me "How come the ground is flat, but the Earth is round?".

My first thought was "What a great question!" My second thought was "Ooh, if I answer that, I can put a big fat check mark next to 'science' for homeschooling today."

So, I rounded up several balls of different sizes from the playroom (Ha ha, pun fully intended.) I showed her how I could curve my finger around the smallest ball. However, when I lay my finger on the balls of increasing size, my finger curved less and less. Finally on the largest ball, my finger was almost flat. Then I explained that the ground seems flat because the Earth is such a huge ball.

Here is Sparkle with the assorted balls. Her finger is curved around a small pink ball.