Why does my 4 year old child get colds all the time?

Allergies likely. Even normal children have a significant number of colds once they start attending day care. The most common condition linked to increase number of respiratory infections is not well controlled allergic disease. Less likely are abnormal architecture of face bones (e.g. High palate), and even less common are immunology and other genetic defects such as cystic fibrosis. Medical evaluation recommended.