Being that young, they need time to build their immune system so having them fight a cold is not necessarily a bad thing. Granted, you don't want them to be constantly fighting as that will take a toll on their little bodies.
In addition to what others said about ensuring they get enough rest, fluids, washing - a couple more things I'd add are the following:
1. If they are running a fever, do not give them something to stop it (at least not unless the fever gets really high, like 102-103). Reason is the purpose of a fever is the body's mechanism for killing the bacteria/virus causing the cold. If you stop the fever, you are stopping their body's natural way of fighting the cold.
2. If they are not running a fever (and even if they are), try to make them as warm as possible. Reason is heat kills bacteria/viruses. If there is no fever or a low grade fever, elevating their body temperature externally will also help - basically creating a "fake" fever. Increased body temperature should assist in killing the infection they are fighting.
3. Double check to be sure what they are exhibiting is really a cold. Often times they are allergies which can appear to be constant colds. I've had that issue - where I think I'm coming down with a cold, but it turns out to be allergies. After having lived for this for a while, I've learned to treat for allergies first, and if that doesn't work, then treat for a cold. I rarely get sick myself, but I do suffer from allergies. The suggestion of using a humidifier is a good one as in winter, if you are in a climate where you have a lot of heating from a furnace; if the humidity gets too low, that causes cold like/allergy like symptoms. I encountered that too where I thought I had allergies, but turned out the air was simply too dry. Once I got a humidifier going, my "allergies" disappeared.
Hope some of these suggestions help in combinations with the others.