Hotels are trying to do something parents often can’t: keep their teen-age children interested. Several hotels have introduced new activities, programs and menus to appeal to teen-age and pre-teen guests ? and their paying parents. Bjorn Hanson, dean of New York University’s hospitality school, says hotels are trying to build loyalty as early as possible. Teens and younger Millennials have become an influential demographic because they set social trends through their use of Facebook and Twitter, he says.