What is ‘childlike’ faith?

Luther:

Children only know what someone tells them and they believe in that. They simply assume that the promise is true and they give glory to God. But we old fools always keep discussing whether the thing is true, how it is possible, and so on. Sometimes that is not even intentional, and we simply forget that the word is so important. Instead of simply believing, like a child, the devil keeps us busy with bits and bobs. Yes, we are truly poor people.

So the best thing is dying early.