If you're preparing the food the best way to track carbs is to total the carbs in the recipe and then figure out what a portion would be. Kind of a pain in the butt and it's not a perfect science, but over time you'll learn about how many units a particular meal contains. Frankly, I've been carb counting 20 years and still don't do it perfectly. But I'm close maybe 80% of the time. If it's food I eat a lot it's easy.
The best carb source I've found is a little book you can get at WalMart or any bookstore called "The Calorie King Guide to Calories, Fat and Carbohydrates." The are smartphone apps that are helpful too, like the Track 3 diabetes tracker ($6) or LoseIt! (free).
I'm sorry your son is having to go through this, but know that diabetes won't keep him from having a good life. Over time your son will figure out how to make diabetes fit into his life.
Also, next year try to find a diabetes summer camp in your area. Camp is a great chance to meet other kids with D and it will give you a break from managing his diabetes, which is important too.
Take care. -Jenna