On the easy mode, the two most frustrating levels(The one that uses the hell tileset in the last 'episode' and the sewer level) are skipped so the kids can feel accomplished as well(In a test with some kids in my cul-de-sac, this proves to be a good idea). Otherwise, I have no idea.
The Hell tileset is used on Chelonia IV, I think it's the second level on that planet. I believe Jazz complains right off the bat about never having a mission without lava.