After you have studied the skeleton, muscles, digestion, circulation and respiration have the students pretend they are in sick person who needs their help. This is like Fantastic Voyage (the movie)but obviously not so complicated!
Brainstorm ideas on how to use one, two, or all body systems covered in class to make your skit entertaining and informative. The class can be divided into equal groups or size based on interest in a particular body system. Give the groups help on aspects of the body you didn't cover if they want to use them in their skit. Select a narrarator if desired and each group has speaking parts as the organs.
This skit can cover not only the purposes of each vital organ, bones, and muscles, but also the major childhood diseases or problems that occur with smoking, drinking, and drug use. There can be a healthy and a sick lung to tell their stories. You could have a heart that needs a transplant and the healthy heart that will take its place. You can make costumes or have the organs wear signs identifying themselves. You may want to have doctors who perform the surgeries or set the broken bones. Whatever you have time for. If you can get help from other people in your building to make props you won't have to spend time doing that.