The basic reason behind why you should introduce your child to photography is that it makes your child more attentive, creative and also increases the observing power. You should introduce it with a very simple approach. Start by gifting a simple camera. Initially just teach him how to click pictures and see how your child goes about it. Allow your child to just focus on something and hit the click button. You also do not need to download the pictures and print it, unless your child is really into it.
Take your child out to different places for examples, a park or maybe a walk and ask him to shoot pictures. This invariably will give you the idea how interested your child is in photography. If your child is interested, take time out to teach your child. You can teach a few rules about focusing the camera, moving closer to the object, positioning and even give a few tips on camera care. While you do this, you shall always encourage your child to be creative. Slowly, as your child grows up introduce your child to different modes that are available and how to experiment with it. You will eventually find your child turning a shutterbug.