Final answer:
The nurse would administer the oxygen to the child when the oxygen saturation drops below the prescribed level.
Step-by-step explanation:
The nurse would administer the oxygen to the child when the oxygen saturation drops below the prescribed level. When the oxygen saturation in the blood decreases, it indicates that the child's body is not receiving enough oxygen. By administering oxygen, the nurse can increase the amount of oxygen in the child's blood, helping to alleviate symptoms and support the child's overall health.