G.K. Chesterton once said that the old stories were about heroes among dragons, while the new ones are all about dragons among dragons. He was talking about the modernist propensity for exploring man's psyche rather than the more enduring theme of Good vs. Evil—more enduring because it's more substantive, and more interesting because it involves genuine conflict.
The older stories are the ones we like. This isn't a petting zoo for merely metaphorical dragons; the monsters here are real fire-breathing wyrms, and the heroes that fight them are flesh-and-blood sword-wielding warriors. Okay, there are a few exceptions (the My Father's Dragon books, for instance), but they're the rarity.
In the Bible, dragons are always bad. Satan is a dragon, and his primary mission is to destroy the bodies and souls of God's faithful elect, as well as anyone else he can burn to a cinder with sin and selfishness. Such creatures shouldn't be allowed to roam the earth, and as Christ's soldiers we're called to do battle with all the forces of evil, not to make friends with them.
We hope you'll enjoy these stories both as stories and as metaphors. The whole "man-fights-dragon" story is one of the oldest in the world, but it still isn't worn-out or boring. Kids need to hear tales like these, to be shown that life isn't just some extended picnic we can romp through carefree. It's war, and if they know how to take down a dragon the way Sigurd or St. George did, chances are they'll be able to fight long and successfully themselves.