Nothing worries us more than have our child suffer. It's so scarry to hear our children wheezing from a nagging cough. I'd suggest you try my hot toddy recipe. I've used it on my children and now use it on my grandchildren when they start coughing, it's so much safer than using all that cold and cough medicine you buy over-the-counter at drugstores. Everyday you hear about them recalling those drugs because of the side effects.
You can find my hot toddy recipe if you go to the left column and look for the button that says "Home Remedies" then scroll down and look for the link that says, "Home Remedy for Chest Congestion and Nagging Cough". It works especially nice if you add it to a cup of hot tea at night, like lemonbalm, but any tea will do and just let your child sip on it before going to bed. You can give it by the teaspoon through the day or anytime you child starts coughing through the night.
I'd also use a vaporizer through the night and anywhere you child is playing during the day. Just make sure you just use a pinch of sea salt in the water, nothing else!