Final answer:
Given the description of the lesions and the absence of associated symptoms or systemic conditions, impetigo is the most likely diagnosis for the six-year-old patient.
Step-by-step explanation:
The six-year-old patient presenting with circumscribed suppurative lesions on the earlobe and knuckles, which resemble cigarette burns, is most likely suffering from impetigo. Impetigo is a common and highly contagious skin infection that can present with pustules and vesicles, which tend to rupture and form a yellowish crust, often seen around the nose and mouth but can occur on any part of the body. In contrast, battered child syndrome would present with a pattern of physical injuries indicative of abuse. Osteogenesis imperfecta is characterized by brittle bones that are easily broken, Münchhausen syndrome by proxy involves a caregiver inducing or fabricating symptoms in a child for attention, and von Willebrand disease is a bleeding disorder, none of which match the symptoms described.
Conditions like ringworm can be ruled out due to lack of the described itching and characteristic ring-shaped rash, while acute otitis media (AOM) refers to an ear infection which presents with ear pain and does not typically cause superficial skin lesions. The cooperative and coherent response of the parents lessens the likelihood of battered child syndrome, emphasizing the aspect where skin lesions alone guide us towards impetigo for the diagnosis.