I don't think this is right...
 

I was out on a hike tonight and picked up a little snake. Sort of looks like a midland brown snake according to a species guide online but I may be wrong. Anyway, a little boy who was holding it dropped it in the grass and it burrowed. The boy started to pull it out, not gently, and yanked it from the grass. I took it back and noticed it had these bumps around its tail, but they would fix themselves after a few moments. Is this natural or is it injured? Would it have been from the boy's roughness with it?

There is a chance those are unborn snakes. They usually give "live" birth in summer so maybe that is what you are seeing?

It could also be an injury...if the spine looked like it had been damaged that might be a better clue.