It is common for antibiotics, including amoxicillin, to cause side effects such as nausea, vomiting, and diarrhea. Giving the antibiotic with food can help reduce the risk of diarrhea. Diarrhea occurs because the antibiotic disrupts the balance of "good" bacteria in the intestines. You can consider supplementing with probiotics to help restore the intestinal flora. Make sure to keep your child well hydrated with a rehydration solution as diarrhea can lead to dehydration. The diarrhea should stop once the antibiotic course is finished. If your child experiences a high fever, blood in the stool, frequent watery stools, or signs of dehydration, consult a doctor immediately.