Shortness of breath or difficulty in breathing can be from various reasons. If your child breaths heavily then it can be from following reasons:

  1. Nasal blockage
  2. Swelling/ infection in the throat
  3. Large tonsils or adenoids
  4. Swelling of the trachea(windpipe)
  5. Swelling of airways (as in asthma or bronchitis)
  6. Infection of the lungs (pneumonia)

The child needs to be examined carefully by a pediatrician.