Once a child is starting to swim on his or her own and is not afraid of the pool's deep end, you can teach the child how to dive.
Take the child to a point in the pool where it is deep enough to dive safely. Explain carefully why you are in the deep end. Emphasize that the child must "never, ever, dive in the shallow end." Children who are afraid to enter the deep end are not yet ready to learn to dive.
Teach the child to dive from one knee first.
Kneel on one knee at the very edge of the pool. Point your arms straight over your head, with your shoulders by your ears.
Put your chin to your chest and lean forward from the waist, trying to touch your fingertips to the water.
Keep leaning until you are almost falling, and then push off with your leg and follow your fingertips into the water, diving in gently.
Demonstrate this first, and then help the child into the proper position.
Assist the child to dive head first into the water.
Practice several kneeling dives until the child is comfortable entering head first.
Demonstrate the same steps from a standing position, bending at the waist and following your fingers into the water. Keep your head between your arms and tuck your chin to your chest.
Assist the child with the standing dive, and repeat until the child is comfortable diving on his or her own.