It is generally recommended to consult a doctor if a cough persists for more than 3 weeks to rule out other possible causes such as acid reflux, asthma, or allergies. It is important to monitor your child's symptoms and overall well-being, and if they seem stable despite the cough, it may not be urgent to see a doctor, but it is still important to schedule an appointment with your child's healthcare provider to investigate the cause of the persistent cough. Avoid giving over-the-counter cough syrups containing antitussives to children under 6 years old without consulting a healthcare professional first. It is always best to seek medical advice to ensure the appropriate care for your child.