I'm guessing here but it sounds like the teacher would like your son to draw a picture of something happening (a cause) and a second picture that shows what happened as a result of the first picture. So, if he's studying home safety right now, a cause picture might be a picture of someone reaching toward a hot pan on a stove and the effect picture might be the same person with a bandage on his finger.
Another cause picture could be one person giving another person a present and the effect picture could be the recipient's face with a big smile on it.
If you're talking about nutrition in your house, a cause picture could be a picture of someone eating a big pile of unhealthy food and the effect picture could be that person having a stomach ache or being fatter than he was in the first picture.
to draw a cause and effect picture. first picture draw the rain falling second picture a a man under an umbrella or a child in hospital as the second picture and for the first picture draw a child eating something with flies around