名詞 infantilism:

1. an abnormal condition in which an older child or adult retains infantile characteristics
2. infantile behavior in mature persons

in.fan.til.ism

n.（名詞）
A state of arrested development in an adult, characterized by retention of infantile mentality, accompanied by stunted growth and sexual immaturity, and often by dwarfism.
幼稚病：一種出現(xiàn)于成年人當中的發(fā)育停滯的狀態(tài)，其特點是思維幼稚，伴有發(fā)育不良和性方面的不成熟，還有侏儒現(xiàn)象發(fā)生

Extreme immaturity, as in behavior or character:
幼稚型：如在行為或性格上表現(xiàn)的特別不成熟：
例句：
.infantilism, which is the subtext of so much American cinema and culture.(John Simon)
.幼稚病是許多美國電影和文化的特征.(約翰·西蒙)

An infantile act or remark.
幼稚行為：幼稚的行為或言論