Try sticking your ear up to their lungs and see if you can hear anything. If you can hear nice clear air noises, that is great. If you hear whistles or squeaky noises, that may mean the lungs are involved. More than half the time this won't work and you won't be able to hear anything, but once in a while parents are able to get some important clues from the "ear to chest" evaluation.
Any baby less then 2 months old is probably worth a visit to the office with their first cold, unless they are eating really well and seem completely happy. It is certainly at least worth a call to the nurse.
For older kids don't minimize the value of chicken soup!
For night coughs try a bit of Vicks Vaporub on the feet!
Another very good thing to do for folks who are old enough is to use a Neti Pot or sinus irrigation
11/15 new tip!!! One of my moms swears by the Oogiebear nose and ear cleaners. These are safe, soft little plastic scoops that allow you to remove stubborn little boogies
Good hand washing is of course essential.
Wishing you a back to school season that is kind and gentle.