Q. A 3-year-old boy is brought to his pediatrician by his parents because of persistent bleeding from mouth after falling on his face while he was playing in the park. He has a history of recurrent nosebleeds but has not had developmental motor abnormalities. On clinical examination, his vital signs are normal, he is alert and interactive, and has a normal neurological exam. On dermatological exam, there are diffuse petechiae and purpura over his trunk and extremities. The pediatrician orders laboratory testing: * Bleeding time is increased * The PT and PTT are normal * The platelet count is normal * The platelet morphology is normal * Adding ristocetin to the blood sample causes platelets to aggregate (normal test). What is the most likely diagnosis?