I thought it was because they had nothing to lose in taking large risks with other people's money but your theory sounds much less childish.

It might be as well to sound a bit childish, and even slightly simple.

In the light of his son's argument, her reason sounded crazy and childish.

If that sounds a little childish, you're right again.

Every defense or argument that came to mind sounded childish and weak.

I wanted to say, "You started it," but that would sound childish.

She can sound almost childish in her deference to him.

Would it sound too childish to say that I'm really going to miss the action?

Make up all the details you want; just be sure to sound very childish.

It sounded childish even to me, but he stopped laughing.