My 6-year old daughter Samani was sad that a friend had spoken a little harshly to her. After the sadness lingered over two days, we tried talking her out of it, but it didn't work. Finally, I had this conversation with her.

Me: Are you feeling sad?
She: Yes.
Me: Would you like to stop feeling sad?
She: Yes.
Me: Then you will have to let it go.
She: How?

Pause... Suddenly, I remembered a conversation with my professor.

Me: Ok -- you will have to repeat what I say, and then the sadness will disappear. Will you?
She: Yes.
Me: "I am feeling sad."
She: "I am feeling sad."
Me: Actually, I am having the thought "sad".
She: Actually, I am having the thought "sad". [Her expression partially changes from sadness to one of curiosity]
Me: Actually, the thought "sad" is having me!
She: Actually, the thought "sad" is having me! [Her expression fully changes to curiosity and astomnishment]
Me: It is eating me up! Gobble, gobble, gobble! [I act it out]
She: It is eating me up! Gobble, gobble, gobble! [She acts it out much more animatedly and with giggles]
Me: Gobble, gobble, gobble! Gobble, gobble, gobble! [I hit my groove]
She: Gobble, gobble, gobble! Gobble, gobble, gobble! [She hits hers, more giggles]
Me: But wait, I am a princess. And princesses face their fears!
She: But wait, I am a princess. And princesses face their fears! [This is a familiar refrain in my princess stories, so she knows what's coming next]
Me: Sadness, you can't gobble me up anymore! Go away! [The mock warrior expression comes on, with a mock sword]
She: Sadness, you can't gobble me up anymore! Go away! [The mock warrior expression comes on for her too, with a mock sword, and a huge confident smile]
Me: What do you think sadness does now? [In my earlier stories, it's a human-eating goblin who runs away when confronted and even turns vegetarian. I know she remembers it]
She: Sadness runs far away and never comes back!!

We both burst out laughing. No more sadness.

Later, I realize this is a useful template for myself, to be used for anger, sadness, ... :).