Like adults, babies can breathe through their mouths if they’re stuffed up, but a congested baby is a miserable baby. Even once babies sleep through the night, an annoying cold can have them waking up constantly. To help relieve congestion, use a small spritz of an over-the-counter saline spray to lubricate the nose. Then use a nasal aspirator to clear the mucus. It has a nozzle that you put in one of the baby’s nostrils and a tube that connects to a mouthpiece you suck on to remove the mucus (seems gross, I know, but the filter will prevent the mucus from going into your mouth). You can safely suction your child’s nose a few times a day as needed.
You can also help your baby sleep more comfortably by running a humidifier or elevating the head of the mattress by putting a textbook or binder underneath to allow better sinus drainage and less dripping in the back of the throat. This works well for babies who are not yet crawling around the crib. Your baby should still be on a firm, flat surface, just at a slight angle of about 30 degrees.