Alopecia Areata: This is an autoimmune condition that can cause patchy hair loss. It's relatively common in children and can occur at any age, including in toddlers. The onset can be sudden, and it may be triggered by stress or other autoimmune conditions.

Tinea Capitis (Ringworm of the Scalp): A fungal infection that causes hair loss, often accompanied by redness, itching, and scaling of the scalp. It's contagious and common in children.
Traumatic Alopecia: Hair loss due to mechanical stress such as tight braiding, ponytails, or excessive heat styling, though less common in boys, it can occur due to accidental pulling or traction.
Nutritional Deficiencies: Deficiencies in vitamins like biotin, vitamin D, or minerals such as zinc can lead to hair loss. This is more likely if the child has a restricted diet or malabsorption issues.

Congenital Hypothyroidism: Untreated hypothyroidism can lead to hair loss among other symptoms. Early detection is crucial for treatment and preventing long-term effects.
Congenital Syphilis: Though rare, it can cause hair loss along with other systemic symptoms. It's critical to diagnose and treat to prevent further complications.

Trichotillomania: A psychological disorder characterized by an irresistible urge to pull out one's own hair, leading to noticeable hair loss. It's rare in toddlers but can occur.
Kerion: A severe form of tinea capitis that can cause significant inflammation and hair loss. It requires prompt antifungal treatment.
Autoimmune Disorders (e.g., Lupus): Though extremely rare in toddlers, systemic lupus erythematosus or other autoimmune diseases can cause hair loss among a myriad of other symptoms.
Genetic Disorders (e.g., Congenital Alopecia): Certain genetic conditions can result in hair loss from birth or early childhood. These are rare and often associated with other physical anomalies.