Can i put eucalyptus oil in my 7 month old baby's cool mist humidifier?

Yes: This is a very nice way to improve the humidity and also help decongest a baby without giving them medications. Don't forget the baby can use nasal saline drops too if congested. Put a couple of drops in the nose, gently massage, and then if he or she doesn't sneeze them out, use the bulb suctioner to clear out. Remember lots of cuddles too when baby not feeling well.

I don't recommend it: I find these scented mists often aggravate a infants's cough and may lead to more nasal congestion. It probably doesn't bother those older than 5 or so but even then i consider it air pollution.