The most common leukocytoclastic vasculitis affecting children is

Henoch Schonlein PurpuraSystemic vasculitis syndrome involving small and medium size vesselsUsually seen in children (in fact it is the most common small vessel vasculitis in children)Vasculitis is caused by immune complex depositionSystemic manifestationSkinJointsAbdominal visceraRenal vasculatureTypical palpable purpuric skin lesionMost common over buttocks and exterior surface of legs and armsAhralgiaColicky abdominal pain associated with nausea, vomiting, diarrhea/constipation Melena or HematemesisProteinuria Microscopic hematuria with RBC cast in urine (Glomerulonephritis) Nephrotic syndromeMost common antibody seen in these immune complexes is IgA (IgA levels are elevated)Platelet count is normal or elevated Serum complements levels are normalPrognosis is excellent and disease is self-limiting. Lasts about six weeks and resolve without sequelae.Treatment involves administration of glucocoicoids(Prednisolone).(Refer: Harrison's Principles of Internal Medicine, 18th edition, pg no: 2797)