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What is The commonest cause of Bacterial Pneumonia in children is – and explain in detail?
Pneumonia 

Pneumonia is an inflammation of the parenchyma of lungs.
Most of the infective pneumonia is caused by bacteria and viruses.

Bacterial causes

Streptococcus pneumoniae (pneumococci) is the most common bacterial pathogens followed by chlamydia pneumonia and mycoplasma pneumonia. — Nelson 18th /e 1795
So, the three most common bacterial causes are → Pneumococci, Mycoplasma pneumoniae, Chlamydia pneumonia
Other bacteria → Streptococcus pyogenes, Staphylococcus aureus, H. influenzae