K.L.
MRI's can be a great diagnostic tool for some circumstances. I practice natural therapies and prefer MRI's over Xray as it is so perfectly safe. But, with the number of reasons for headaches, I would not expect there is a great chance the MRI will provide the information you need in order to identify a real solution.
I live in your area and I work with a chiropractor that is very, very good with children and one of the most educated and experienced doctors I've ever known. He is a radiologist as well as a chiropractor and is an expert nutritionist as well. I have seen him stop chronic conditions, from siezure disorders to headaches, for many children when medical doctors had failed to find a cure. His name is Dr. Duane Marquart and his office, Primary Care Chiropractic, is located near Hwy. 141 and Manchester Road.
Whatever the MRI indicates, you might want to discuss the results with Dr. Marquart. He is very good at helping you understand your options before settling on a plan for treatment.
Best of luck to you and your precious first-grader.