Yeah, whoever above said you don't have to know any rare genetic diseases besides Downs and neurofibromatosis did not have my test (or just didn't notice the more rare diseases mentioned). UWorld was amazing preparation. Everything on UWorld is fair game. Pretest, however, is excessive.
The best advice I could give is to read Peds in Review articles on every patient you have on the wards. If you have outpatient specialty clinics, read the Peds in Review article about the most common diseases in that specialty.
This shelf is NOT all bread and butter. It's a GOOD MIX of bread and butter, rare disease, neonatal, adolescent, subspecialty, trauma, surgery, and pathophysiology.