Like all people living in the future society of "Harrison Bergeron," Harrison's parents have substantial external handicaps on their bodies to prevent them from being exceptional in any way. Because of this, and because they are in fact quite intelligent, the handicaps are programmed to distract and disorient them, causing problems with their short-term memories. Both Hazel and George watch Harrison's rebellion on live TV, and then his death at the hands of the Handicapper General; sadly, they are unable to remember the event past a few seconds.
"You been crying" [George] said to Hazel.
"Yup," she said.
"What about?" he said.
"I forget," she said. "Something real sad on television."
"What was it?" he said.
"It's all kind of mixed up in my mind," said Hazel.
"Forget sad things," said George.
"I always do," said Hazel.
(Vonnegut, "Harrison Bergeron," tnellen.com)
Their reaction is typical of the people living in the future; they cannot change their stations in life, because of the handicap laws, and they can't even remember important events. Instead, they simply "forget sad things," and continue with their lives. This means that not only was Harrison's sacrifice in vain, but his parents no longer remember that he died, and so assume that he, like them, still lives a handicapped and average life.