Final answer:
The highest priority nursing intervention for a child with leukemia is following guidelines for protective isolation to prevent infections.
Step-by-step explanation:
The highest priority nursing intervention for a child with leukemia would be following guidelines for protective isolation. Leukemia is a type of cancer that weakens the immune system, making the child more susceptible to infections. Therefore, it is crucial to take precautions to prevent exposure to pathogens. This may include maintaining a sterile environment, implementing hand hygiene practices, and limiting visitors.