1.  infantilism(n = noun.state) - an abnormal condition in which an older child or adult retains infantile characteristics;
is a kind of abnormalcy, abnormality
has particulars: ateleiosis, ateliosis

2.  infantilism(n = noun.act) - infantile behavior in mature persons;
is a kind of misbehavior, misbehaviour, misdeed

infantilism, n.
1 childish behaviour.
2 Psychol. the persistence of infantile characteristics or behaviour in adult life.