Big difference between “religious” and “Christian”. Don’t know about the generosity of kids, but Christian adults are the most generous of all groups. (And, whether the Oregonian is aware of it or not, Atheism is a religion in its own right.)
I have seen other data on charitable contributions by state that undermines this claim. Red states in the Bible Belt and Midwest invariably give more per-capita to charities than blue Liberal states in the Northeast or on the Left Coast.