Final answer:
The correct advice is to bring the immunocompromised child to the physician's office due to the increased risk of serious infection that his mild symptoms may indicate.
Step-by-step explanation:
The most appropriate instruction for the mother of a 3-year-old boy on chemotherapy complaining of a sore throat, malaise, and a temperature of 99.8 degrees F would be to plan to bring the child into the physician's office today. Children receiving chemotherapy are immunocompromised and at higher risk for complications from infections. Therefore, even mild symptoms like a sore throat and low-grade fever could signify a more serious underlying condition that requires prompt medical evaluation.
Options such as giving aspirin should be avoided due to the association of Reye's syndrome with aspirin use in children with viral infections and also because any medication should be taken under the guidance of a physician with a child undergoing chemotherapy. Monitoring the temperature and only worrying if it gets above 104 degrees F or keeping the child warm might not address potential complications and the urgency needed in managing the symptoms of an immunocompromised child.