The answer is foreign body aspiration

Foreign body aspiration is the most common cause of recurrent pneumonia in an otherwise healthy 3 yo child. Becoz of the lung's anatomy,the rt.side is more common for aspiration.
Immunodeficinecy disorders........recurrent infections by oppurtunistic organisms+failure to thrive
Cystic fibrosis....failure to thrive, malabsorption,clubbing
Chediak higashi.....recurrent infections of skin & mucous membranes & RS, albinism.
Congenital lung abnormalities......present at a much earlier age.