Stick them up where they can be noticed and will be read. A teacher told me she clipped one of my newspaper columns out and mailed it to her teenager. He never knew where it came from and thought one of his friends or teachers were trying to tell him something. He got the message, and since his mother never mailed him letters, she was never suspected of sending it. If your children can't read, draw a picture.
Most children know what the happy face and unhappy face look like.
They will surely ask you about it. Sit down and write out your own feelings in a personal letter to yourself, or it can be addressed to the one who is making you upset. It really does make a person feel better. And sure, I use my kid's crayons. Try your hand at painting.