Alopecia Areata: This is an autoimmune condition that leads to patchy hair loss. It's common in children and can present as a single bald patch or multiple patches. The onset can be sudden, and it often affects the scalp, though it can occur on other parts of the body as well.

Tinea Capitis (Ringworm of the Scalp): A fungal infection that causes hair loss, redness, and itching. It's contagious and common in children.
Trichotillomania: A psychological disorder where the individual pulls out their own hair, leading to noticeable hair loss. It can be a response to stress or anxiety.
Nutritional Deficiencies: Deficiencies in nutrients like iron, zinc, or biotin can lead to hair loss. These deficiencies can be due to a poor diet or underlying conditions affecting nutrient absorption.

Cutaneous Metastasis: Although extremely rare in children, metastatic disease to the scalp can cause localized hair loss. It's crucial to consider this in the differential diagnosis due to its severe implications.
Neurofibromatosis Type 1: This genetic disorder can cause hair loss due to neurofibromas (tumors) growing on or under the skin, including the scalp.
SLE (Systemic Lupus Erythematosus): An autoimmune disease that can cause hair loss among many other symptoms. It's less common in children but can have serious health implications.

Aplasia Cutis Congenita: A rare congenital condition characterized by the absence of a portion of the skin, which can include the scalp, leading to bald patches.
Congenital Triangular Alopecia: A rare condition where there is a triangular area of hair loss, usually on the temples, present from birth or early childhood.
Kerion: A severe form of tinea capitis that can cause significant inflammation and hair loss, potentially leading to scarring if not treated properly.

Each of these diagnoses has distinct characteristics and requires a thorough medical evaluation for accurate diagnosis and appropriate treatment.