I agree with Sneezydiva, allergies are the main culprits. Milk was a big offender here...on and off antibiotics for years....put in tubes but didn't help..continued with ear infections...until I took the matter into my own hands. Went total nutritional....health nut time....buy a juicer...cheap one at any store will do...make the base from carrots as they are the cheapest and best juice makers...add what you want...I add greens...lettuce, kale, etc and once they get used to the taste add small piece of garlic(natures antibiotic).
Next prob: how do you get him/her to drink it? little at a time....dropper to small sip ,to small glass, then finally a full glass.
Child can have a multivitamin too.