Origin: bef. 1000; ME
childisch, OE
cildisc. See child, -ish 1 
Related forms: child⋅ish⋅ly, adverb
child⋅ish⋅ness, noun
Synonyms:
Childish, infantile, childlike refer to characteristics or qualities of childhood. The ending -ish often has unfavorable connotations; childish therefore refers to characteristics that are undesirable and unpleasant: childish selfishness, outbursts of temper. Infantile, originally a general word, now often carries an even stronger idea of disapproval or scorn than does childish: infantile reasoning, behavior. The ending -like has pleasing or neutral connotations; childlike therefore refers to the characteristics that are desirable and admirable: childlike innocence, trust.
Antonyms:
mature, adult.