My Father's World explained that it is the largest star that we can see with the naked eye. I wasn't able to confirm that online, but I did find several sites that confirmed that the size of Betelgeuse is about 650 times bigger than the sun.
...Which is why we needed to head outside for the little experiment MFW suggested...
First we drew the sun on a piece of paper shrinking it down to a one-inch diameter. (The dot is the approximate size of the earth comparatively.)
Then we went outside to measure out approximately 650 inches using a yard stick. (Yes, my kids are still in their pajamas.)
In the picture above you can see three of the kids. The two furthest away represent the approximate diameter of Betelgeuse in comparison to our one-inch sun. A7 is in the middle holding our picture of the sun.
Here's a close-up.