Allergic Rhinitis: This is often the most common cause of dark circles in children, resulting from chronic nasal congestion and allergic reactions which lead to increased blood flow and visibility of the veins under the thin skin around the eyes.

Atopic Dermatitis (Eczema): Children with atopic dermatitis may have dark circles due to the chronic rubbing and scratching of the eyes, leading to increased pigmentation and swelling.
Nasal Congestion: Similar to allergic rhinitis, any cause of nasal congestion (such as a cold or sinus infection) can lead to dark circles due to the increased venous pressure and pooling of blood.
Sleep Deprivation: Lack of adequate sleep or poor sleep quality can cause paleness, puffiness, or dark circles under the eyes in children.
Anemia: Iron deficiency anemia is a common condition in pediatrics that can cause pale skin and dark circles under the eyes due to the lack of hemoglobin.

Thyroid Disorders: Both hypothyroidism and hyperthyroidism can cause changes in skin pigmentation and eye appearance, including dark circles.
Kidney Disease: Certain kidney diseases can lead to fluid retention and puffiness, including around the eyes.
Hematological Malignancies: Though rare, conditions like leukemia can cause anemia, fatigue, and consequently dark circles under the eyes.

Neurofibromatosis Type 1: This genetic disorder can cause changes in skin pigmentation, including café-au-lait spots, which might be mistaken for dark circles.
Mucopolysaccharidoses: These are a group of rare genetic disorders that can cause a variety of symptoms, including clouded corneas and changes in facial features that might include dark circles under the eyes.
Lymphatic Malformations: Rare conditions affecting the lymphatic system can cause swelling and discoloration around the eyes.