Back-kicking
It is necessary to perform the skill of kicking on the back before a child attempts to do any backstroke arms. Back-kicking uses different muscles than freestyle kicking, incorporating the core or ‘abdominal’ muscles not only to move the legs, but also to stabilize the body and keep the head fairly still. When starting it is really important to kick softly and do small kicks with the feet. As the swimmer gets better the kicks can increase in speed and power.
4 easy steps to Back-kicking:

1. Floating on board
2. Kicking drills
3. Supported board kick
4. Independent board kick