The pups learn the activity from the poor mother that has been kept caged all her life. The mom does it out of boredom and stress. Imagine being in such a torture chamber all your life, never let out and being used as a never ending breeding machine!
They should discourage the licking. Tell the baby no and redirect to some other activity like a toy or some play. It may seem impossible but it is very treatable if dealt with early in life. It does take constant repetition and consistency. Teaching the puppy how to play fetch and other things to keep it busy will help. Maybe get her some bully sticks or other healthy chew toys (no rawhide....dangerous stuff) to help her redirect to chewing may help.