We go the natural route, so we don't use the OTC meds. Fortunately, we nip it in the bud before it can get that far. You can get the Emergen-C drink mix in the pharmacy section at Wal Mart and give at the first sign of a runny nose. We first tried this when our daughter was 2yo and she could handle 2000mg of the Vitamin C drink a day and it kept the runny nose away...you would never know. We had her keep this up for a week or a week and a half and then lightened up on the drink.
This is what we do for congestion though:
Humidifier is wonderful (all night long and throughout the naps)
Nebulizer with colloidal silver (used this for croup and pneumonia as well)
Eucalyptus oil (if you get neat, put in a carrier oil before applying) and apply on chest and feet
Lung and Bronchial formula found at www.herbsfirst.com. You can get the extract or capsules. Wonderful stuff! Even my asthma husband uses this...he has never had any prescription!
I know many of my friends that LOVE cutting up an onion and placing it on the chest. Make sure you apply olive oil first and then put the onions on the chest and wrap with ace bandage or something like that to keep it in place. With all of these things, I bet you have onions. Some wrap it in a sock and stick it to the chest and then bind it down with an ace bandage. It's up to you.
I know it's hard to see such a little one having difficulty breathing. I hope he is well soon. Good luck!