Roger has started an interesting thread at his blog about kids opinions on books, and several commenters have mentioned their experiences with kids in Mock award discussions.
This is the sixth Mock Newbery I’ve helped organize for adults. I’ve taken a couple of stabs at doing it with kids, but have found it nearly impossible in the public library setting (impossible for me. I tip my hat to those who have made it work.). From what I can tell, the successful kid Mock Newbery requires a "captive" audience over a long period of time. I had to ask myself why I was trying to do it. There are a lot of different reasons to run a Mock Newbery…for me, the main satisfaction is in getting other adults excited and informed about the awards. That’s why we keep our shortlist short–because we strictly follow the committee’s actual discussion and voting guidelines, and require voting participants to have read all the titles. I took this model from the CCBC. (It was my partcipation there, and at The Association of Children’s Librarians of Northern California, that helped me develop my critical chops and land an appointment to the Newbery Committee early in my career.)
Meanwhile, I’ve found that I can glean kid opinion on specific titles best by milking the relationships I make with regular library users at the public desk. The young individuals who have grown to trust me give me opinions that I can trust. Without that relationship, most kids will simply tell you what they think you want to hear.