Greetings,
First of all, the required length of the HPM fellowship is one year; several programs offer a 2nd year, usually in research.
http://www.acgme.org/acWebsite/downloads/RRC_FAQ/540_Hospice_and_Palliative_Medicine_FAQs.pdf
There are there are a total of 82 active HPM training programs offering more than 210 fellowship positions.
77 programs have been accredited by the ACGME
http://www.acgme.org/adspublic/ Scroll down under "Family Medicine" (HPM is administered for ACGME under the FM RRC) to click "Hospice and Palliative Medicine."
5 programs have been accredited by the AOA
http://opportunities.osteopathic.org/search/search.cfm.
There are dedicated pediatric palliative medicine positions at:
Children's Hospital Medical Center of Akron
CHOP in Philadelphia
MGH/DF/CHB in Boston
The rest of the programs are required to provide a pediatric palliative experience of apparently unspecified length. So, it varies. What also varies, and this is key, is the amount of elective time, flexibility and support for an individualized fellowship experience that is more evenly balanced and appropriate to the unique training of Med/Peds.
For instance, I recall that the ACGME-accredited HPM fellowship at Indiana University is funded through an endowment (that means your paid time is uncoupled from your "productivity," so things like outside rotations are easier to arrange and justify) and it has a relatively large amount of elective time.
http://medicine.iupui.edu/palliative/
Happy Hunting!