When my daughter was four she was fascinated by doctors (Grandpa was a pediatrician) so she wanted a "Doctor Party"   We asked each guest to wear a "lab coat" made out of a white adult shirt worn backwards.  As each guest arrived, he or she was given a "medical record"--a manila folder with a computer-generated "health chart" for each child.    For activities we weighed and measured each child, let each listen to his or her heart with a real stethoscope, took each's temperature with one of those ear thermometers, and entered the data on their medical records. There were also stuffed animals and dolls for "patients" and ace bandages and toy doctor kit supplies to take care of the patients.     I had each child lay down on the floor on a roll of brown paper and traced around their bodies. Then they could color in their features and there were construction paper organs (heart, liver, lungs, brain, etc.) for them to paste on their "anatomy" chart. It was fun to see where some of the organs ended up! For the cake, I made a sheet cake with dark chocolate frosting and piped "bones" in white frosting so that it looked like an X-ray.    We served healthy snacks. The "goodie bags" included tongue depressors, surgical masks and caps (thanks to my father-in-law) along with some candies and other small party favors.  The "medical records" went home with each child too. Everyone had a great time. My advice is to keep the party small (we had 5 kids total) and to write out the schedule to keep things flowing along.