ấu trĩ in English:

He wasn't enjoying the occasion so he thought he'd spoil it for everyone else - it was very childish of him.

childish behaviour

Marcin is childish

Such a childish plan is bound to fail.

When I became a man I put away childish things, including the fear of childishness and the desire to be very grown up.

He was so childish that he couldn't resist temptation.

Age does not make us childish, as they say. It only finds us true children still.

Women are directly adapted to act as the nurses and educators of our early childhood, for the simple reason that they themselves are childish, foolish, and short-sighted.

Peter was fed up with childish girls.

When an average person sends a message in a bottle, it's just a childish fantasy. When Christopher Columbus sends a message in a bottle, the fate of an entire country is at stake.

When I was a kid, I thought that if I died the world would just disappear. What a childish delusion! I just couldn't accept that the world could continue to exist without me.

They are a very childish sort of people, I think.

Embarassed at having been caught telling such a childish fib (...).

It isn't mature for a grown-up to act irresponsibly. It is childish.

My father can be terribly childish, but he means well.