Hi Cory.
My question is do you only have the WSM? For my Son's first birthday, I grilled a bunch of wings, burgers, smoked Sausages and hot dogs. I did ribs in the WSM the day before, and sauced and lightly grilled them to heat them up. It turned out great. If you can use a grill along with the WSM then a lot of wings may be easier and cheaper than quarters or thighs. I tried to have a lot of finger and kids foods. The ribs were eaten by the adults, but the kids loved the burgers, dogs and wings.
I'm certainly not trying to change your menu or have you deviate from your original plan. I know that my WSM alone would not have cut it for the amount of food that I cooked, unless the food was cooked in advance and reheated before the party. If that is your only option, then I would go with thighs, but that is just a personal preference.
I hope this helps.
Derek