KidsCrypt let you swap letters to hide your text.
Shifting letters is one of the simplest and most widely known encryption techniques. Just pick a letter to swap and your whole text will be ciphered accordingly. Even the roman emperor Julius Caesar used to cipher his messages by this method. If you know the key you may decipher it even without the app.
To cipher text just press the eye. To decipher paste in ciphered Text. If the key is not included or you do not know the key you may test them all. The app does not save any content.