OK. What about? Show a picture of a person swimmimg and say "Can". Then show a picture of a person who can't swim, who is sinking in water, and say "Can't". Then show a picture of a person skating and say "Can". The show a picture of a person skating who has fallen down while skating and say "Can't", and so on. Go through about 4 or 5 sets of pictures. <You can find such pictures on clipart sites>
Make sure they show different activities, like writing, say writing chinese characters, speaking a language, say Spanish and/or French, using a computer, painting a picture, drawing, mountain climbing, flying a plane, and so on. Find funny ones too, like eating an elephant.
For the first 2 sets of pictures say one word "can/can't". For the next sets of pictures make the phrases longer: He/She can/can't, and for the last few sets of pictures use sentences: He/She can/can't skate.
After you teach the ideas "can" and "can't", move on to question formation by asking students if they can do the activities in the pictures; e.g. Can you...? Yes, I can/ No, I can't. After that, show students things that you, the teacher, can do, like wiggle your ears without using your hands, roll your tongue, pat your head and rub your stomach at the same time, etc. Have the students try too. See if they "can" or "can't" do what you can do. It's a lot of fun! Then ask the students if they would like to come up one by one and show the class what they can do. Have the other students try. See if they can or can't do it and have them say so out loud.
Finally, go through the can/can't flashcards sets again and have the students tell you if they can or can't do those acts; e.g., I can; I can't. My father can, My brother can, etc.
You could also put the students in groups and ask them to come up with 2 or 3 actions that they think you the teacher can't do but they can do.
I did that lesson with elementary school students about 3 years ago and they just loved it. One of the examples of things they came up with that a teacher can't do was "A teacher can't hit the students."
All the best.
activities: can/can't 
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