Meanings of so puerile in English

It all seems to me so empty, so unreal, so puerile.

That hope justifies my cruel studies, which, though apparently so puerile, are in reality worthy of serious consideration.

It seemed so ridiculous, so puerile to have to go through with this political farce in order that a natural economic evolution might be achieved.

We drove through the noisy streets, and Frenchmen never before or since showed themselves to such small advantage-sopuerile, so petty, so vain.