Hello I have gone through your question and understand your concern. The symptoms and chest x ray results are suggestive of pleural effusion secondary to pneumonia. It is very common for children to catch up pneumonia due to bacterial or viral infections which can lead to accumulation of fluid in lungs known as pleural effusion. Expected treatment is confirmation of diagnosis using various diagnostic test like chest x ray in lying position to see the fluid levels, blood test to check infection, sputum culture, CT scan of thorax and treatment involves a full course of antibiotics if bacterial infection is the cause. In some patients the fluid accumulated needs drainage which is a minor procedure. Thank you.