Impetigo: A common, highly contagious skin infection in infants and young children, characterized by a pustular rash and often accompanied by fever. The presence of a pustular rash and fever in a 9-month-old makes impetigo a leading consideration due to its prevalence and the age of the patient.

Eczema Herpeticum: A complication of atopic dermatitis (eczema) where the skin becomes infected with the herpes simplex virus, leading to a pustular rash and fever. Given the age and potential for underlying eczema, this is a plausible diagnosis.
Folliculitis: An inflammation of the hair follicles, which can present with pustules and fever, especially if caused by a bacterial infection. This condition is common in children and could explain the symptoms.
Scabies: A parasitic infection caused by the mite Sarcoptes scabiei, which can lead to a pustular rash, particularly in areas like the hands, feet, and genital area, and may be accompanied by fever. Scabies is highly contagious and can affect infants.

Staphylococcal Scalded Skin Syndrome (SSSS): A serious condition caused by staphylococcal toxins that can lead to widespread skin lesions, fever, and potential dehydration. It's crucial to identify SSSS early due to its severity and risk of complications.
Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a petechial or pustular rash, fever, and potentially life-threatening complications if not promptly treated. Although less common, the potential severity makes it a "do not miss" diagnosis.
Kawasaki Disease: An acute febrile illness of childhood characterized by fever, rash, mucous membrane changes, and potential for cardiac complications. The presence of fever and rash, even if pustular, warrants consideration of Kawasaki disease due to its importance in preventing long-term cardiac issues.

Congenital Syphilis: A condition that occurs when a child is born with syphilis, a bacterial infection usually acquired from the mother during pregnancy. It can cause a variety of symptoms, including skin rashes. Although rare in areas with good prenatal care, it remains a consideration in the differential diagnosis due to its potential severity and the importance of early treatment.
Leiner's Disease: A rare condition associated with severe eczema, recurrent infections, and failure to thrive, often linked to immunodeficiency. The presence of a severe pustular rash and fever could suggest an underlying immunodeficiency or rare condition like Leiner's disease.