hello, gud evening, as per the descriptions , ur child may be having an upper respiratory tract
infection, because foul smell comes mostly because of infection or bad oral hygiene
. check the child s body temperature, check his nostrils for any foreign body lodged in his nose accidentally- ground nut or peas or any small objects, check his oral cavity for any discharge, regarding the treatment- only supportive care can be advised on the query right now- like clearing his nasal cavity
with salaine nasal drops, steam inhalation , oral hygiene, maintainin his nutrition status, most of all examination by a doctor in person very much important .