Fever and cough are very common ailments in children. Most of the times it is caused by certain viruses. Some children are more prone to repeatedly catching cold but the propensity comes down with age. His tonsils need to be evaluated as increase in size of the tonsils could often be related to such frequent episodes of catching cold. Tonsillitis could be associated with recurrent episodes of cough and cold. If the episodes are too frequent, surgery may be required, but not otherwise. The treatment of fever is use of plain paracetamol to reduce temperature. Usually it is associated with an allergic component and use of some antiallergic like cetirizine should help. Antibiotics are generally not required as they are ineffective against viruses. It should recover on its own in 5-7 days. Steam inhalation should be helpful in diluting the cough. For the episodes of diarrhoea or vomiting, proper replenishment of the lost salts and water needs to be done the the use of ORS. You have to add a full sachet in the designated amount of water (200 ml or 1 litre depending on the size of the sachet). It needs to be given sip by sip. Antibiotics are not needed unless associated with bloody diarrhoea. I do not think that it is serious. But in case the child becomes lethargic or does not feed well, I insist that you take him to your doctor.