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.
Like the adult type of skin yeast infection, infant yeast infections can also be caused by the same type of yeast which is candida albicans. For diaper yeast infections, since infants have fragile skin, their urine and stool (poop) may cause an irritation due to the acidity of both.