Someone asked this recently, and this was my response:
This is one of those topics that is so frustrating, because I am reading all about how the kids can't handle watching someone else open presents, they might get bored, they'd rather play...well, what about kids learning that sometimes it's all about SOMEONE ELSE and not ME! I think the presents should be opened, because someone picked it out...another good lesson, it's better to GIVE than to receive. People want to see the gift they bought opened. Also, someone mentioned that the toys might get opened and pieces lost....again, is there no control or expectations of the kids. someone can put the toys away after the wrapping is gone. when we have low expectations for our kids to learn these social lessons, they will meet them.
This was her update after the party:
After reading all the helpful responses, I had completely planned to not open presents at the party, but I would still ask the guests we could open their child's gift if they felt their child wanted to see my child do so. So, we were at the party and it got close to the end, and I felt like we needed to open gifts! It just didn't seem right to not do so and my mother-in-law suggested that we do so during the cake and ice cream. Well, it turned out beautifully!! My husband first brought the child who brought whichever gift we were opening up at the time and set him/her next to my son. Then I opened the gift for my son while he ate his cake and ice cream. Then, held up the gift and my husband took a picture of gift, son, and gift-giver (it helped to keep track of who gave what gift as I wrote thank you cards). A lot of the kids gathered around, and many would point to the gift excitedly and say, "I brought that one!" It was perfect. Wrote all the thank you cards that same evening. So glad for all your suggestions, and this turned out just the right way! :)