What are the side effects of children taking fever-reducing medication?

Patient's question:

Symptoms: High fever
Onset time: November 16
Child weighs 15 kg
At 19:00, due to a high fever of 38.7°C, he was given Melin 1.5 droppers (the instructions say to take 2 droppers). At first, it was thought to be a fever, so another pack of Hutarong was given (taken in the recommended amount), along with a pack of Cefixime granules. However, as far as I know, Hutarong also has fever-reducing effects, so will taking Melin and Hutarong together cause any side effects?
Third day at 0:35, high fever of 39.1°C, Hutarong and Cefixime were given (same dosage as before); at 3:30, Melin 1.5 droppers were given. At 8:00, the doctor confirmed it was herpangina and administered an IV drip.
Assistance needed: Will there be any side effects for a 2-year-old child? How should I use medication in the future?

Doctor's answer:

Now diagnosed with herpangina, which is caused by a viral infection. It can be treated with drugs such as Dianqingkailing injection, Ribavirin injection, Yanhunning, penicillin, etc. Continuous treatment for several days should allow it to heal on its own. During the infusion period, if the child's temperature drops below 38.0°C again, they will also need to take fever-reducing medication.
Lifestyle care: Encourage the child to drink more water, avoid spicy and extremely cold foods, pay attention to preventing colds, and take measures to prevent fever.