I was trying to share some "facts" with my 7-year-old daughter about the nature of our solar system and our place within the Milky Way galaxy. The title of this post sums up her response. What she was challenging me on was the size of the Milky Way galaxy. I told her it was probably thousands of light-years across (and I explained carefully what a light-year was). Pulling a "thousands of light-years across" number out my head wasn't exactly accurate. Turns out it's more like 100,000 ly in diameter.
She picked up on my uncertainty and challenged me. Our conversation that followed involved how to trust and verify information and how to question someone about what they know. I looked up the exact diameter of our galaxy on Wikipedia. She then asked, "How do they know it is correct?". She eventually accepted my advice to be more trusting of information from scientists whose work has been verified by other scientists. But also that she should continue to question things like this and when in doubt to verify it for herself.
She was amused that her seemingly infallible father could be wrong about something. To her it seems that I know everything. It won't take long now for her to realize I know very little about everything--along with everyone else.