Contact Dermatitis: This is a common condition in children, often caused by exposure to irritants or allergens such as soap, detergent, or certain plants. The fact that it's localized to one hand suggests a localized exposure.

Eczema (Atopic Dermatitis): A chronic condition characterized by itchy, inflamed skin. It's common in children and can be localized to one area, such as a hand.
Impetigo: A contagious bacterial skin infection that can cause red sores on the skin, often on the face but can appear on hands. It's common in children.
Insect Bite or Sting: Children often play outdoors and can be prone to insect bites or stings, which can cause localized rashes.

Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth of the skin. It requires prompt antibiotic treatment to prevent serious complications.
Herpes Simplex Virus (HSV) Infection: Can cause a painful rash and is contagious. In rare cases, it can lead to more serious infections if not treated.
Scabies: A parasitic infection caused by the scabies mite, leading to intense itching and a pustular rash. It's highly contagious and requires specific treatment.

Kawasaki Disease: Although rare, it's an important diagnosis to consider in children with a rash, as it can lead to serious cardiac complications if not treated promptly. It's characterized by fever, rash, swelling of hands and feet, and other symptoms.
Juvenile Idiopathic Arthritis (JIA): Can sometimes present with a rash, although it's more commonly associated with joint symptoms. It's an autoimmune condition that requires specific management.
Pityriasis Rosea: A skin condition that causes a rash, often starting with a single patch (herald patch) followed by an eruption of smaller patches. It's usually self-limiting but can be uncomfortable.