If a child has low bone mass, parents can take several steps: 1. Ensure the child gets plenty of sunlight, as it helps the body produce vitamin D, which is crucial for calcium absorption. 2. Encourage the child to participate in outdoor activities and moderate exercise, which promotes bone health. 3. Include calcium and vitamin D-rich foods in their diet, such as milk, eggs, fish, and leafy green vegetables. 4. If dietary intake is insufficient, consider calcium or vitamin D supplements under a doctor's guidance.