We got off to a good start, but I eventually took O's gloves off (I had her wear gloves so she wouldn't burn herself) since it was hard for her to color with them on. Mistake! She accidentally touched a rock and burned her finger. I think it scared her more than anything since it didn't even leave a mark, but I felt awful. She didn't want to participate in the activity after that, but she didn't mind giving me directions on finishing the rest of the rocks :) She was ready to color more rocks after they had cooled off, and she was disappointed when it didn't work.
This is not a project I would recommend for 2 year olds! But we did have fun despite O's injury :)
To make the hot crayon rocks, heat your rocks on a foil lined cookie sheet at 350 degrees for 15 minutes. We then placed them on a cutting board, and colored them with crayons (with the papers peeled off). Oh, and don't let your kids remove their gloves or oven mitts!