When another word is added to the front of a word, the meaning of the word changes. Usually, it changes into the opposite of what the original word meant, or into a word that negates the original word. For example; unhappy means not happy, unserious means not serious. Give your child some more examples to make sure that they completely understand what you are trying to teach them. Then, help them trace the un- in each word, and read the word aloud with them.