别这么孩子气！

Don't be so ___childish!

与成年人相比，他们的争论显得相当幼稚。

Compared to adults, their arguments seemed rather ___childish.

因为一点小争执就拒绝和某人说话，这很幼稚。

It's ___childish to refuse to talk to someone after a minor disagreement.