Besides the fact that child insurance generally pays lower than adult insurance, there are not too many procedures that a pediatric rheumatologist can do (Procedural specialties are better paid by Insurance companies than cognitive or non-procedural ones).
As per this 2011 Pediatric Rheumatology Workforce Study published on the U.S. Dept. of Health site says,
"Pediatric rheumatologists attribute the current shortage to low salaries, inadequate reimbursement, and poor working conditions. the median salary for a pediatric rheumatologist at the assistant professor level was $115,022, which was comparable to other cognitive pediatric subspecialties - however, it is far below salaries for intensivist and procedural pediatric specialties, such as neonatology ($155,202), pediatric critical care ($144,933), pediatric cardiology ($149,159)"The other specialty averages mentioned in the quote above also refer to the same assistant professor level. And sure enough, if you had checked the University Missouri Columbia Physician salaries data that I had posted before, the only Assistant Professor in Child Health / Rheumatology is enlisted as making around 114,000$ a year.
It's easy to see that the salaries in pediatric rheumatology work out pretty much the same (and at times lower) than a pediatrician who has not done any fellowship training - in other words the financial return on investment (ROI) is almost nil - a big reason for shortage of pediatric rheutmatologists across the United states. And despite the shortage, the demand driven higher salaries may not be seen soon since children with joint problems are often seen by the adult rheumatology physicians (i.e. Internists specialized in rheumatology)
Two characteristics about the pediatric rheumatologist workforce in America: First, They are mostly female and Second, a big proportion are International Medical graduates. Given the low-end incomes, it is not surprising that the American medical grads are not too crazy about the field. And that's why many residency programs in Pediatrics considered to be a IMG friendly.
How to Become a Pediatric Rheumatologist in USA?
Here are steps to become a Pediatric Rheumatologist:
1. Undergraduate School after High School : 4 years (For American Medical Students)
2. Medical School : 4 years
3. Residency in Pediatrics : 3 Years (IMGs start here in US)
4. Fellowship in pediatric rheumatology : 3 Years.
How to Prepare for USMLE Step 1? Read USMLE Step 1 Preparation Books Review.