The nursery rhyme I hear Thunder is the perfect song to sing when it is thunder and lightning. Try to explain to the kids that thunder and lightning can be frightening, but not dangerous if they are at home or in a safe place. But tell them that they never must go bathing outdoor during a thunderstorm.
This song has the same tune as the good old rhyme Where is Thumbkin?.
Tip: Ask the kids what they think I Hear Thunder is. Do they understand it is a egg? :)