You asked

When should I take my child to the doctor if they have a cold?

If your child has a cold, there is no need to bring her to the doctor. The common cold is caused by viruses which cannot be cured by antibiotics. However, if you feel that your child is displaying symptoms that are more severe than those that typically present as part of a cold, then you should consult with a doctor.  For instance, if your child has a fever which has lasted for more than three days, you should schedule a visit with your GP.
When the body is trying to fight off a viral infection, its natural defences are lowered, the immune system is weakened leaving the body open to secondary bacterial infections.
If your child is also complaining of an ear ache, a stiff neck, increased nasal congestion or a chesty cough that is accompanied by difficulty breathing, then these can all be signs of a secondary bacterial infection which may require an antibiotic.

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