When I first heard about being able to tell the temperature by crickets I really thought people were trying to pull my leg. I grew up around plenty of crickets and plenty of high temperatures and had never heard of this. It turns out this chirp counting is not only true, but has been around since 1837. It's called Dolbear's Law after the scientist who figured out that the air temperature influenced the rate of cricket chirps. To experiment with this, count the number of cricket chirps in 15 seconds and then add 40. The number that you get will be a rough estimate of the temperature in degrees Fahrenheit. If you have a thermometer handy you can check and see how accurately this works for your family and your backyard crickets.
Kids might also be interested to learn that crickets don't chirp with their mouths, but use their wings to make the sound. Only the male crickets chirp, usually to attract and court females, but also to sound a danger alert.
My father taught me to count the number of seconds between a lightning flash and hearing thunder. Again, I don't think it is exactly accurate, but it must be a fairly good estimate. Sounds, like thunder, can travel a little more than one mile in five seconds. So for each five seconds you count between seeing lightning and hearing thunder, that means the lightning strike was a mile away. So ten seconds is two miles, fifteen seconds would be three miles, and so on. The reason you see the lightning first is that light travels at 186,000 miles in a second, while sound travels one fifth of a mile in that same second. That's hard for kids to understand, but it's a good science lesson. And if nothing else, they will be so busy counting that they won't worry so much about the storm.