Children who can’t jump off the ground at the age of four may be normal or abnormal, such as hip dysplasia and spinal muscular atrophy. 1. Normal phenomenon: If other aspects are normal, such as intellectual development, language expression ability, walking, etc., this situation is considered normal phenomenon, can not jump feet off the ground may be related to the usual sports less. 2. Abnormal: (1) Hip dysplasia: Hip dysplasia is the development of the hip joint of the affected children lagging behind or defective, resulting in the femoral head and acetabular part of the abnormality, there will be lower limb activity disorders, unequal length of the lower limbs, lack of side force and other symptoms. (2) spinal muscular atrophy: if accompanied by an unsteady gait, frequent falls, difficulty in going up and down the stairs, and the symptoms gradually aggravate, this situation is abnormal, considering spinal muscular atrophy, due to the atrophy of the muscles, the child will not be able to jump with both feet off the ground. Children 4 years old can not jump off the ground on both feet can go to the hospital for examination, according to the situation of the correct treatment.