Synonyms of 'infantile'
childishDictionary, immature, puerile
This kind of humour is infantile and boring.
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Babyish actions, feelings, or looks are like a baby's, or are immature.
I'm ashamed of the babyish nonsense I write.
If you describe someone as immature, you are being critical of them because they do not behave in a sensible or responsible way.
You're just being childish and immature.
Thesaurus for infantile from the Collins English Thesaurus
Infantile behaviour or illnesses are typical of very young children.