Sharon,
Here is a suggestion, how about coating the doll with Petroleum
jelly and casting in plaster of paris. That will give you the negative
imprint. Do several different positions have the kids choose one to
work with and make a positive to be "toga-ed" with plaster. I wonder if
you coated the negative imprint with wax if you could use that as a mold
release, if not more petroleum jelly.
Ellen