In my family, we always open presents in front of the giver so we can say thank you and they can see our reaction to the gift. This sometimes means getting presents before or after Christmas. For example, we won't see my grandparents until the dsy after boxing day so DD (18 months) will get presents from them then.
My husbands family seem to open all the presents on Christmas day and then do a general "thanks for all the presents" when they see us. I don't know if the kids even know which gifts were from us or if they're just a general bunch of presents. We have spent (quite a lot of) money on gifts but don't see the kids open their presents or play with them. This year we will see them on boxing day, WIBU to keep their kids presents to open that day? WIBU to ask them not to give DD her presents until we see them? DH says he doesn't know, so I was wondering if other families do the same and how you would feel.