FWIW, my opinions are:
1. Yes, you are supposed to have backspin such that the rotation is a true 4-seam rotation. There are drills that help teach this and reinforce this. If a kid isn't doing it, he may not be alone, but that's no reason not to teach him to throw properly. Or the other kids, for that matter.
2. It may not be pure 12/6 rotation. Depending on arm angle it may be tilted a bit. But it should be true to the 4-seam aspect irrespective of the angle of release.
3. 4-seam rotation is more true than 2-seam rotation or a ball just thrown with disregard for grip. But no throw is completely straight, and all throwers are genetically unique such that everyone's ball will move a little bit differently from the next guy's. Such things keep it all interesting!