Viral Exanthem (e.g., Roseola, Fifth Disease): This is often the most common cause of rashes in infants and toddlers, characterized by a widespread rash that can appear after a fever. The high incidence of viral infections in this age group due to their developing immune system and frequent exposure to pathogens makes viral exanthems a leading diagnosis.

Atopic Dermatitis (Eczema): A common condition in infants, characterized by itchy, inflamed skin. It often starts in the first six months but can persist or begin at any time during infancy.
Contact Dermatitis: This can occur due to an allergic reaction or irritation from substances like soaps, detergents, or certain fabrics. It's common in areas exposed to these potential allergens or irritants.
Impetigo: A contagious bacterial skin infection that can cause red sores on the face, especially around a child's nose and mouth, though it can spread to other areas of the body via touch, clothing, and other items that come into contact with the sores.

Meningococcemia: Although rare, this condition is life-threatening and requires immediate medical attention. It's characterized by a rash that can start as small, red-purple spots that quickly spread and can develop into large bruises. The rash is often accompanied by fever, headache, and stiff neck.
Kawasaki Disease: An acute illness that predominantly affects children under the age of five. It's characterized by fever, rash, swelling of hands and feet, redness of the whites of the eyes, lips, and tongue. If untreated, it can lead to serious cardiac complications.
Staphylococcal Scalded Skin Syndrome (SSSS): Caused by staphylococcal toxins that typically affect infants and young children, leading to widespread skin lesions and exfoliation, resembling scalded skin.

Juvenile Rheumatoid Arthritis (JRA): Now more commonly referred to as Juvenile Idiopathic Arthritis (JIA), this condition can present with a rash, among other symptoms like joint pain and swelling. The rash is typically pink, faint, and may appear during fever spikes.
Langerhans Cell Histiocytosis: A rare disorder in which the body accumulates too many immature Langerhans cells (a type of immune cell). Skin rashes can be one of the presenting symptoms, along with bone lesions, and other systemic manifestations.