B cells are a specific type of white blood cell called a lymphocyte. Other types of lymphocytes include T cells and natural killer cells. B cells develop from stem cells in bone marrow. They remain in the bone marrow until they become mature.
Infantile behavior is something the masses are taught to exemplify since childhood. As adults they (mostly Betas) are encouraged to have sexual relations with multiple partners.
Sometimes the child is kept naive and vulnerable so that they believe they will be unable to survive without the narcissistic parent. This is called infantilization and the child relies on the support of the parent, no matter how awful their life may be with them.