Place an apple on the desk behind you before starting the lesson.
Hold your hand out in front of you with the palms up to show that they are empty.
Announce to your students that you have "no apple." Ask if they understand that you have "no apple," emphasizing the two words.
Put the apple in your hand and say, "Now, I don't have 'no apple' because I have an apple." Ask the child if you have no apple. Again you will need to emphasize the words "no apple." Wait for a response. They may respond with just "No" or replay that you have an apple.
Let the children hear you repeat the following: "Now I don't have no apple because I have an apple." See if they understand the idea that when you create a double negative, the two negatives cancel each other out. This is the core to teaching double negatives.
Take time to discuss various possibilities. One example uses what happens in everyday life. If you or your students had a recent illness, you can use the example that involves that illness by saying, "I have no fever. Yesterday I took my temperature, and I didn't have no fever because it was 105 degrees." (You can use any number above normal, but it should be higher than the normal body temperature.)
Wait for the children to mention that this sounds funny. Tell them that you are showing why you don't use two words that say no together. Explain that while it may seem you are saying that you don't have an apple or a fever, you are really saying that you do.
See if they completely understand before asking for a better way of phasing that you have the apple. Watch for the signs of understanding when you teach double negatives.
Attempt to illicit an answer that eliminates negatives. Create lists of phrases with double negatives, such as "I don't now nothing." Ask your child to tell you what the sentence actually says. Ask her to tell you what she thinks the writer meant to say. Have the child rewrite the sentence correctly.