26 synonyms for childish such as foolish, adolescent, babyish, and fatuous. Childish is an adjective, and its antonyms are mature and sophisticated.
Adolescent, boyish, bread-and-butter, child's, childlike, children's, girlish, teenage, teenaged, young, young-looking, and youthful.
Babyish, fatuous, foolish, immature, inane, infantile, irresponsible, jejune, juvenile, naive, puerile, silly, and stupid.