We have the same issue and have tried several things including letting them go into the computer lab and play the games for a while at the beginning.  What we have used for the last few years though is a Bible Trivia Card that has 3 questions on the story we are learning.  The questions are simple and have three choices that the kids can choose from to circle for the answer. We include the scripture where the answer can be found.  This gets parents, kids and shepherds into the Bible as they arrive and the kids are also aware of the story we are learning if they missed the previous week. When we do the group opening we go through the questions and give each child a small piece of candy for their efforts.