Children’s toenails are thick and bulging mainly caused by diseases, common diseases include onychomycosis, nail malnutrition and so on. 1. Ringworm of the nail: ringworm of the nail is a disease caused by dermatophytes invading the nail plate or under the nail, and ringworm of the foot, impaired immunity and other factors can induce ringworm of the nail. After microbial infection, the toenail can appear rough thickening, brittleness increase, destruction of shedding and other phenomena. 2. Nail dystrophy: Nail dystrophy is an abnormality in which the normal formation process of the nail plate is impeded due to various reasons, and it is often related to psoriasis, lupus erythematosus, drug allergy and other factors. Children with nail dystrophy will show symptoms such as toenail thickening, roughness and nail peeling. Children with thick and bulging toenails may also have other causes, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.