First Focus, a children’s advocacy organization, wants the U.S. Department of Housing and Urban Development to change its definition of homelessness because 81 percent of homeless youths are essentially invisible under the current guidelines, the group said in a statement released Monday. The department doesn’t consider children living temporarily in hotels or motels or “doubled-up” with friends or extended family members as being homeless, making ineligible for certain services such as shelter or short-term housing.