My opinion is I could not have got thru the 1st 6 years of my kids lives without using cough medicine. I am so glad the whole "no meds before 6" came out after mine were past 6 yrs old. I have never been one to just give meds & I was always careful about giving the right dose. These new rules were put out because so many kids were given the wrong meds dose they decided to tell all parents not to medicate. Crazy!
I would try to keep my kids off meds all day - coughing is needed, they need to cough it up. So unless they were exhausted from coughing & feeling terrible, no meds during the day. Then would give robitussin DM at night to help thin the mucus & suppress that awful urge to cough all night. This helped them get much needed sleep.
I would also do vicks vaporub on their chests. Raise their mattress at their head by putting a phone book under the mattress where their pillow is. This helps them breathe easier.
Good luck!