I like what susan had to say, and that is pretty much what I do.
I have the Vicks vaporizor that you can add eucalyptus or rosemary oil to, or Vicks makes some stuff you can put in the water which gives it kind of the vicks smell to open up and loosen up the gunk. I use it anytime my daughter is stuffy or has a runny nose. Plus, it warms the air and makes them more comfortable. Concern is that it has a hot coil, so you need to put it out of reach of the child or turn it off when they are awake. I, personally don't like the cool mist ones, they make the room really cold and you risk mold in the filter and machine.
Hope that helps.