It is not uncommon for a child to still have a fever on day 6 of taking antibiotics. Antibiotics can typically take 48 to 72 hours to start working against a bacterial infection. If the fever persists, it could be due to a viral infection like a cold. It is important to monitor their condition and you can safely give them Tylenol if necessary. If you have any more questions or concerns, it is best to consult a healthcare professional.