Physiatrists are doctors that help patients with their rehabiliation process. They are sometimes called "PM &R" doctors which stands for "physical medicine and rehabilitation". I often refer my clients to these doctors, especially when the child has multiple impairments including neurological, orthopedic, visual, and mental delays such as with cerebral palsy or certain syndromes. I also refer clients to them when I know something is going on with the child but I'm not sure whether to send them to an orthopedist or neurologist. I think physiatrists are well versed in different areas of disabilities therefore they may be the best professional to steer the family a particular direction. Here is a link to their professional organization:
AAPM&R - What is a Physiatrist?
I also think it is nice to have a physiatrist for the medically fragile child, because the need for adaptive equipment, assistive technology, and other functional items tends to get pushed to the bottom of the list for a sicker child, especially when the parents of the child have a variety of specialty doctors they are seeing on a regular basis. The physiatrist is the "one in charge" and facilitates the communication of all doctors and other professionals once the child is stabilized from the medical problems.