Humidifier during baby's colds
I use a hot/cold humidifier during my baby's cold, and I think it helps because it keeps her nasal passages moist, which helps to keep the mucus from drying and blocking her breathing. You can buy one or the other, or a humidifier that does both. With a hot humidifier, you do have to worry about baby potentially getting into it and getting harmed.
If you can't buy a humidifier, a steamy bathroom can accomplish the same thing, but not as constantly (unless you want to spend day and night in the bathroom).