Your child may develop some gastrointestinal side effects depending on the amount of iron content it has and may develop yellow urine for some time. Single capsule may not bother much I assume and may not require any active intervention without any symptom. However, you should consult a pediatrician if any complaints. Or if you think he has consumed more capsules, you should seek a consult immediately.
Next Steps
consult a pediatrician if any symptoms
Health Tips
look for abdominal pain, diarrhea, vomiting, blood in stool.