in·fan·til·ism 
(ĭnfən-tl-ĭz′əm, ĭn-făntl-)
(ĭnfən-tl-ĭz′əm, ĭn-făntl-)n.
1. The existence of juvenile physical or psychological characteristics in an adult, as from failure to develop secondary sexual characteristics.
2.
a. Marked immaturity, as in behavior or character.
b. An infantile act or remark.
3. A condition in which one desires to act or be treated like a baby, sometimes associated with a paraphilia.