It depends a lot on what prior knowledge they have in programming and how much time you got. Here are some general tips

• Learning becomes easy if it is connected with existing knowledge. So pick a problem they are already know how to solve it in a hard way and show how programming can make it easier.
• Include some tricks that will trigger surprise and curiosity. For eg. reading this post to see how used a trick to teach binary numbers.
• Incorporate some games to make it fun.
• Include some quizzes to make it interactive and to check their understanding.
• Try to make them do hands-on programming using some physical materials (like Montessori work).