Character names starting with the same alphabet would work fine for kids as it's a very good device for making them to remember the story. Especially if the names rhyme. Otherwise, for adult readers, it would appear less creative on the part of the writer. Also, names can be fat and thin, boring and interesting, formal and jazzy, traditional and modern, just based on the personality traits of the characters. Many times, names, as such, convey a certain personality. And hence, using the personalities, the author can arrive at a suitable name. How a name sounds very much impacts action scenes. Wouldn't it be great if historical fiction characters had "heavy" first and second names, as heavy as their clothing, and pulling down page lines from both ends?