Final answer:
The non-rebreather mask is the most reliable oxygen delivery system to provide a high concentration of inspired oxygen to a 7-year-old child.
Step-by-step explanation:
The oxygen delivery system that most reliably delivers a high (≥90%) concentration of inspired oxygen to a 7-year-old child is the non-rebreather mask.
This mask consists of a reservoir bag that fills with oxygen and two one-way valves that prevent the child from rebreathing exhaled air or room air. The oxygen from the reservoir bag is delivered directly to the child's lungs, ensuring a high concentration of inspired oxygen.
Other oxygen delivery systems like nasal cannula or simple face mask may not provide as high of a concentration of inspired oxygen, especially if the child has high oxygen requirements.