Onecan 150 Tablet contains fluconazole, which does pass into breast milk in small amounts. A single 150 mg dose is generally considered safe during breastfeeding when prescribed by a doctor, and since your child is 4 years old, the risk is lower compared to younger infants. However, this medicine should only be taken under medical supervision and not as self‑medication. If your child shows any unusual symptoms, such as stomach upset, diarrhoea, or a rash, after taking the medicine, consult a doctor promptly.