Bone density is an important indicator to explain the strength of bones. It simply means that when there is a shortage of minerals in the bones, it leads to osteoporosis, increased brittleness and easy fractures. However, since children are in their growing years, they generally do not have low bone density, so are bone density tests for children harmful? Through the children’s bone density examination, can further grasp the child’s body lacks what necessary growth elements, early detection and early treatment. Bone density is an important indicator of bone quality, reflecting the degree of osteoporosis and an important basis for predicting the risk of fracture. Regular measurement of bone density for children can prevent calcium deficiency and help children supplement calcium through dietary adjustments. Bone density test for children is mainly conducted by ultrasound, which is non-radioactive and non-invasive, so it is harmless to children. Bone density test results often indicate the possibility of calcium deficiency in children. A low bone density test result often indicates that a child may have a calcium deficiency. However, the level of bone density does not always correlate with calcium deficiency, and sometimes children with calcium deficiency do not necessarily have low bone density. On the contrary, normal children are often found to have low BMD. Therefore, it is important to take into account the child’s clinical presentation and other laboratory findings to determine whether the child is deficient in calcium.