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.
Infant - various definitions. Toddler - older. Explanation: In medicine, an infant is a child under 12 months (at least in the UK). However, in UK schools, the 'infant years' are (or used to be - the system is different now from when I was at school!) the period from ages 4 to 7. The child would then progress to junior school (often within the same school) at age 7. 'Toddler', as far as I know, has no definition in medicine and is colloquially used of a child who is big enough to walk but is still considered a baby - 'toddling' is the kind of unsteady walking associated with young children.