The Play's the Thing: Strawberry is made to feel self-conscious about an old, patched-together rain coat that she has. When the kids put on a play version of Cinderella, Strawberry and the others are able to see that it's not what you wear that counts, but what you are.
The Costume Party: Peppermint Fizz wants to exclude a new girl, Blueberry Muffin, because she's "different" - in the way she looks, lives, talks, etc. When a dress-up party is set-up, Strawberry gets the other kids to play a prank on Peppermint that makes her see the value in even being different