Arch dysplasia in 3-year-old babies may be caused by congenital developmental abnormalities, or it may be related to trauma, rheumatism and various other factors. 1. Congenital developmental abnormality, if the baby’s genetic mutation occurs in the process of development, it may lead to the development of the foot arch is affected, and the symptoms of foot arch hypoplasia appear. 2. Trauma, some babies with hypoplastic arches may be related to trauma. If the baby has been hit by external force before, resulting in nerve damage, it may lead to contracture and weakness of tendons, and thus this symptom will appear. 3. Rheumatism, some babies with rheumatism may have abnormal arch development due to the impact on the immune system, which may lead to this symptom. If arch dysplasia has already occurred, it is recommended to seek medical treatment as soon as possible to avoid complications in the later stages.