Healthy babies kick as a way of exercising their small bones. Humans are not immobile beings naturally. Whenever you get the chance to sit near a new born kid, you will often notice how restless the baby can be-kicking arms and legs occasionally. Babies stop moving their bodies only when they are asleep, they are always smiling.
When it comes to how regularly they should be kicking, it depends on the baby concerned. One of the good things about pregnancy is that the mother knows a lot about the baby before it comes forth. She knows when the baby is sleeping and when she is awake. Some provider's advice a pregnant woman to count the number of kicks late in the pregnancy, and record the time it takes to record up to ten kicks when the baby is busy and active.
My advice to most clients is to drink some orange juice, lie on their side, and pay attention to the baby whenever the baby seems less active. If the baby is not active at all, I advice they call my attention.
But also remember that as pregnancy matures, there is less room for the baby in there, so expect more squirming and less kicking because it also counts.