Well the obvious answer:

"What do they teach you in that church of yours?!"

"They teach me not to ridicule other people's religions. Don't they teach that at yours?"

But of course what kid can think of such things on the spot?

But speaking of thinking of things on the spot, this is a true story. A child was being ridiculed for being a Christian in a public school in Memphis, Tennessee (it happens even in the Bible Belt!). After a bit of abuse, the teacher said, "You just believe because your parents believe!"

The kid, showing what I thought was perfect presence-of-mind, replied, "I'm only 11 years old! I think that's perfectly appropriate!"

Smart kid. Teacher should be fired, though.

Alex