Most think humans will reach Mars within their lifetimes. Many expect to make the trip themselves. And rock climbing will be tops among recreational activities. Such are the aspirations of thousands of U.S. schoolchildren. More than 2,600 youngsters took part in the online poll, released Thursday by the organizers of Space Day, an annual event designed to bolster interest in science, math and space among youths. “It’s exciting and encouraging that the spirit of exploration is alive and that students see it occurring in their lifetime,” said Orlando Figueroa, director of NASA’s Mars Exploration program. “These may well be the children that make it a reality.”