I'm glad your son is okay- we'll keep praying for him. Having one's jaw broken is no picnic. I had my jaw broken and wired shut for two months and it was the worst thing that ever happened to me. It's amazing how much you miss being able to chew your food. It becomes an all-consuming preoccupation when you can't do it- you dream of chowing down on hamburgers, crunching carrots etc. I lost 30 pounds with my jaw wired shut, it was horrible (I went from 150 to 120)- I looked like a famine refugee towards the end. I was always a skinny guy who didn't care about food until I couldn't have any for 2months. After that, I began to enjoy food much, much more. I no longer weigh anything near 150 pounds!
Buy your son some cases of Ensure, and Slim-Fast, and the weight-gainer protein shakes that bodybuilders use. That'll keep him going. If there are any gaps large enough in his mouth- he can squirt that Easy-cheese stuff in the can through the opening. Your son seems like a tough kid, hopefully he'll pull through like a champ.
All the best,
Andy