Children usually remain well until they are 6 months of age.
There after they start getting infections off and on, some more than others.
The reason is that babies get immunity against common viral infections from their mothers while in utero. However this immunity wanes off by 6 months. Thereafter the child will fall ill whenever he comes in contact with viruses or bacteria.
Most of the time these are respiratory tract infections, cold, cough and fever, at times diarrhea and vomiting also.
These are usually self limiting infections, and children get better in 3 to 5 days. Usually only paracetamol is required to make the child comfortable. Antibiotics have no role to play in viral infections and should be avoided.
There are few precautions you can take to try to reduce the no of these attacks.
1. See that you child gets well balanced diet, including fruits containing vitamin C.
2. Child should get plenty of rest.
3. Child also should get enough exercise.
4. As far as possible, see that your child avoids coming in contact with someone who has colds and coughs.
For more information do look up the book easybabycare available at easybabycare.net and read the chapter on diet. You will get an idea as to what sort of diet should be given to child.