This exercise is really easy to do and explain to your children (or even to work on yourself). We can easily identify good feelings when the sun is shining and the weather is good the same way as we can identify difficult or challenging feelings when the days are dark and stormy outside.
The exercise lets us understand that there are times when we cannot change how we feel inside. Like the weather outside, we can't change it.
Just like the weather, it passes. The rain stops, the sun comes out, your mood will also blow over. This exercise allows us to acknowledge our feelings and how we feel without having to react to them.
Comfort them by letting them know when they are going through a stormy day, they can come to you for a hug.