I had no idea DS would want one at 3, but in September when he was in line to meet Buzz in the first hour of our first morning, he saw other older children with autograph books, and let us know that he wanted one, too.
He filled the one we bought on that trip, so I thought we were done, but when we went in December, he asked us to get another one. They aren't that expensive so it wasn't a big deal, but I was still very surprised each time!