We very commonly hear complaints of children having a ''head cold'' from the time of their birth------In many cases, this is due to a Vasomotor Rhinitis or an Allergic Rhinitis.
One of the functions of the nostril is to warm the incoming air to the lungs. This is done by the blood vessels under the lining of the nostrils expanding, so as to bring the warm blood into contact with the colder air. The lining of the nostril therefore becomes swollen, and the nasal passage becomes narrower, hence the stuffy sound.
This condition may therefore be more noticeable at nights when the environmental temperature falls. In the case of allergies, when the kid has an allergic tendency, inhalation of dust, pollens, powder, smoke, fumes from paint etc may irritate the lining of the nostrils which then become swollen, and which then produce mucous-----hence the sniffles.
Home remedy-----normal saline drops may be bought over the counter or made [1 level teaspoon of salt to 2 measuring cups of water].