I've eaten at Boma twice for dinner, and I think it's great for picky eaters! They have plain carved meats, regular child food, are great if you have allergies (they made some plain grilled salmon and plain rice for my DS once, he loved it and ate so well!).
It is a beautiful resort, to visit if you aren't staying there!
We like a glass of their wine also - they have some nice choices.
One thought: if it's a rehearsal dinner, you will have a lot of up and down going through the buffet. We did a big group once there (12 of us, including 6 children) and it was a bit hectic to actually visit with each other. I think for our big group, a regular sit down meal would have been more relaxing to actually talk to each other. With the little kids, we were spending some time helping them go through the line, then getting our food ourselves. We did enjoy the food, though!
If you are staying there, having a club room would be nice, so you can visit in the lounge before or after the meal.
Jiko is another nice option: more expensive, but you are served, and the food was good there also. I think for picky eaters, though, a buffet is good. Just weighing the pros and cons if it's a big group.