First of all, bless your heart! That's a heckuva lotta kids to feed. I'm not sure if you need a one-dish meal or if you could make the parts separately ahead of time and then heat and serve combined to the diners. Either way, I think a chicken broccoli rice casserole (or chicken w/mushroom soup served over rice) might be a good way to go, or at least a change from bbq. This might be filling without being too heavy/spicy for the kids to eat in the hot weather. I wish you the very best!