Okay, so I am one of those in the middle of this problem. I'm a graduate student in pharmacy, and have had courses in complementary and alternative medicine (aka CAM). Additionally, I am a regular chiropractic patient - I get monthly adjustments and it has greatly helped with a neck injury I sustained from an unfortunate endo.

I definitely agree with the suggestions of PubMed, accessing your nearest university library, Google Scholar, etc. I might also suggest that if your nearest university has a medical school you talk to them and see if they have a CAM practitioner to give you a helpful evaluation of the literature. Perhaps it could make a nice project for a student as well.

As far as choosing chiropractors, it sometimes comes down to luck. You might want to look around for one who specializes in NUCA [neck and upper cervical (neck, not cervix) a-something] treatments. I'm surmising your friend assumes your child's affliction is related to the upper spinal cord.

Best of luck in your information quest!