That's a toughie. Boma has a huge variety of food and I love their desserts, soups and meats. Its also nice to see the AKL and go out to the viewing area before or after your meal.
O"Hana has always been good for us and if you get a nice view of the castle that makes it even better. The entertainment is fun, my dd was still into it when she was nine, I doubt she'll participate this trip since she's 11!
I don't think you can make a bad choice. And also know that if the food at O'Hana doesn't appeal to your kids, they will be happy to serve you a kids meal at no extra charge. Sometimes they tell you up front, sometimes they don't!
I don't think you can make a bad choice. O'Hana is more lively, but Boma is always noisy and crowded so I don't consider it really a quiet meal either. But you aren't entertained with the corny Polynesian singer (that I think is pretty funny) either.