What can ammonia in a left lung cause to a 2 year old baby?

Not sure: I suppose you mean pneumonia, not ammonia, as pneumonia is a common lung disease, whereas ammonia is a blood waste product. Pneumonia may be treated and cured or may cause complications such as respiratory failure and result in death or complications such as lung abscess, effusion, sepsis etc. It depends on the bug that caused it, the immune response of the host etc.

Pneumonia: Pneumonia can make a 2 year old to have respiratory difficulty, vomiting, decrease intake and lethargy that night require hospitalization and IV antibiotics.