hái​zi​qì

childish

孩子气 (孩子氣) hái​zi​qì
childish noun
possessing the characteristics or qualities of a child; boyish or immature

He is already in his thirties, but he still talks very childishly.

childishness noun
the trait or quality of being childish or acting like a child

After all these years, his childishness hasn't changed a bit.

Frequency

Movie subtitles
3.04 per million appears in 1% of films
Written text
2.37 per million

Sources

Definitions
CC-CEDICT