Regular salivary flow stops with sleep. This allows mouth germs an opportunity to feed on remaining food particles, old shed mouth lining cells, and stagnant saliva. The byproducts of bacterial metabolism produce the foul odor. We often cannot identify any specific cause.
Mouthwashes are a poor substitute for good oral hygiene.
Oral hygiene is particularly important for any child with bad breath. Floss and brush regularly, which helps remove trapped food particles and promote healthy gums. Regular dental checkups are essential. A thorough medical exam for other oral or especially sinus disease if the teeth and gums are in good shape and clean.