Polycythemia vera very rare in kids but described from age 7 months! More typically age 5-14yrs. 

Haemoglobin range of 15.5 to over 25, with haematocrits from 41-80%.  Yet high values often seen in asymptomatic teenagers. Partly this is because pre-pubertal range is different, but lab can’t know pubertal status so will cut off at an arbitrary age. Our lab gives normal up to 18 for adult males and 16.5 for adult females.

Symptoms are headaches, pruritus, dizziness/syncope.  Serious complications not uncommon, often part of presentation eg Budd-Chiari syndrome, stroke, haemorrhage.  Leukocytosis appears to be associated with higher risk of complications.   Thrombocytosis often seen. 

Molecular studies available. [Ann Hem 2009 PMID PMID: 19468728]