My thought was that it might have had something to do with cost. THe EMT's might have told them that if they were uninsured that it could cost several thousand to travel to the ER by ambulance versus the parents driving them. In that case they would have been saving a lot of money for the family. It also happens a lot that when someone else looks at a person, the injury seems to not be there anymore. Man, I can't tell you how many times this has happened with my pets and the vet. Now I'm not really comparing a child to a dog, but sometimes the pain comes and goes, and the child may not have presented with much pain when the EMT's were present.
The only time I called an ambulance was when I literally couldn't move due to back spasms. I felt really bad about it, but I couldn't move, I was in a level of pain that I didn't know existed, and I was scared that something was wrong with my spinal cord, or that I might cause myself permanent damage.