Infantile behaviour or illnesses are typical of very young children. infantile aggression
disapproval If you accuse someone or something of being infantile, you think that they are foolish and childish. This kind of humour is infantile and boring. = childish
being or befitting or characteristic of an infant; "infantile games" of or relating to infants or infancy; "infantile paralysis
a rare but serious syndrome of childhood characterized by withdrawal and lack of social responsiveness or interest in others and serious linguistic deficits; "there is considerable dispute among specialists concerning infantile autism