I think M has croup.

My internet research is telling me that it's caused by a virus and there's no real treatment or need to go to a doctor as long as he's breathing ok. If he has trouble breathing, we call the doctor. Does that sound right?
ETA: In case anyone is interested, I talked to the pedi and she said they don't need to see him unless he gets worse and really has trouble breathing. They suggested running a humidifier and taking him outside to breathe in cold air if he starts coughing. Hopefully the little guy will get better soon.
Re: Croup
I would call your pedi.
DS brought home a lovely xmas present from daycare, a nasty cold, that he gave to my Dad (who was visiting) and me. I feel your pain!
Off to the beach
DS 7/18/2010
Handy 2.0 Due Early August
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12/17/2011 Christmas Caper 10K
2/11/2012 Have a Heart 5K
3/17/2012 DC RNR Half Marathon
4/22/2012 10M Parkway Classic
10/28/2012 Marine Corps Marathon
We've never had croup and really nothing more than a bad cold, so I definitely don't have firsthand experience, but a coworker of mine's daughter got croup when she was about 2 and it ended up getting really bad to where she was very close to being admitted to the hospital.
Being a new mom, I'd probably go to the doctor just to be safe. I also keep thinking of those (probably a bit alarmist) articles in the parents magazines that talk about the dangers of self-diagnosing and how kids aren't getting treatments they should because parents wait thinking they know what's wrong and it turns out to be something more severe.
I self-diagnose myself all the time with the help of the web, but I try really hard not to do it with DS. I know it's really rare, but if something serious ended up happening I'd be really upset if just a quick trip to the doctor could have prevented it.
I feel like 90% of the time when we go to the pedi for a sick visit, they check him out and say "It's a virus, nothing you can do but let it run it's course." And then I'm out a $25 co-pay and 2-3 hours of sick leave from work, depending on when the appointment is, for basically nothing. Sigh.
DD had croup around 18mo old, it was the middle of the night, we called the pedi who could tell from the phone, from her breathing, that it was croup; we ran a hot shower and then since she didn't get better, took her to the ER. She got nebulizer treatment and had it for a while at home, too. Since it's cold out, you should take him outside and let him breathe in the cold air, it should make his breathing easier. And I would def. take him in to be seen by a pedi!