Boma, unfortunately, is not open for lunch - they only serve breakfast and dinner. Both meals are excellent if you like somewhat "exotic" food and buffets. We have always had good food and service but I would definitely suggest perusing the menu to see if the food there is something you and your family would enjoy!
Boma is spectacular for breakfast and dinner! I highly recommend both! But, from my experience, lunch at the Mara isn't worth trekking to AKL for. If you're there, fine; if not, go to Boma for dinner instead.