ér​xì

trifling matter

儿戏 (兒戲) ér​xì
trifling matter noun
a situation or task treated with a lack of seriousness or responsibility

How can a matter of life and death be treated as child's play?

child's play noun
games played by children

The children were playing simple games on the grass.

Frequency

Movie subtitles
1.73 per million appears in 1% of films
Written text
1.33 per million

Sources

Definitions
CC-CEDICT