I remember going to one when I was a kid, and since it was given by the Girl Scouts, it was done VERY budge friendly...
What they did have was a table set up, with a tarp draped over it so you could not see it as you walked up to it. They had an adult on either side of the table, one to guide and one to explain.
Under the tarp were various bowls filled with stuff...
The first: JELLO, and the person on the side helping the children guides the hand into the bowl and says this is guts and goo...
The second: Cauliflower (whole) that is someones brain
Third, Noodles: Intestines
Fourth: A plastic glove filled with water and you tell them it is a dead hand.
More funny once they realize it is all fun...well at least I know I was about 10 and 24 years later, I still remember it being fun.
GOOD LUCK!!