Use of digital music players is growing among youths, with more than half of those naming iPod as their brand of choice, according to the results of a new study. NPD analyst Anita Frazier, who recently contucted a study called “Kids and Digital Content,” said that “the average age of first use of portable digital music players has declined over the last three years.” According to the study, 31 percent of kids aged 6-10 now…