Spanky, are you all right? A cr80 has no powervalves. I am surprised that the bike still runs. The best scenario is that somehow by a grace of god, all you need is a top end. Worst case and sorry to say that after 2 days the bike is most likely pretty ruined is that it needs a cylinder, top end, crank, and crank bearings. From the way you describe "slime" in the airboot, I would not be looking forward to finding out the results of this 11 year olds folly.
Moral of this story, never let 11 year olds do work on bikes without checking that they did it right!
Also, whenever I hear a bike run without an air filter, it makes a deep intake noise. I am surprised the bike sounded normal!