Dinners in Park City, UT
For a hungry group, I'd suggest Nacho Mama's. It's next to the PC Mariott in Prospector Square. Good tasting Southwestern food with a quantity that will satisfy that post-skiing appetite. It's a small place, but it will accomodate groups.
I'd suggest Grub Steak, too. But, I'll tell you that I know the owner, so I could be biased. It's accomodating of groups, too.
It is also in Prospector Square.
For something on Main Street, I honestly can't think of someplace that would satisfy hungry teens, outside of maybe Main Street Pizza and Pasta. Bandit's BBQ is there, but I think it's overpriced for what you get there - it was much better when it was Texas Red's.
The first reply mentioned Cisero's. We used to go to it every Monday in the "off season" when they had the $5.00 all you can eat spagetti night. But, the times we've gone "in season", we've been disappointed in what we got for the price. It seemed to try to portray an upscale restaurant with mediocre food. Unless you want just spagetti with meat sauce, I wouldn't recommend it.
If you want quick food or something to take back to the condo/hotel, try Spencer's Smokin' Grill BBQ. It's a little place in the strip mall at Bonanza Dr (same strip mall as Einstein's Bagels and El Chubasco Mexican). Ribs, chicken, brisket, pulled pork, smoked sausage. They do individual plates and "family packs".
I had a very good meal at Ciseros, an Italian place on Main Street. Its a casual place. Not too expensive, but good food. http://www.ciseros.com/about.htm
Grub Steakhouse on Sidewinder Dr. was also not bad. I've had better, but it was a pretty good deal. I was there with a bunch of 30-something guys and we all left stuffed. Its a little outside of the downtown area.
Good luck skiing. When I was there last January, it snowed 5 of seven days, three of them over a foot. Best powder of my life.