I haven't read that story in a while, but I believe that George and Lydia Hadley are the parents of two very precocious children who can project their fantasies onto a large screen eerily familiar to our widescreen TVs of today--even though Bradbury wrote his story decades ago.
The screams sound familiar because those screams are George's and Lydia's own. The Hadley's children have been creating violent fantasies about killing their own parents using the technology in the story. Now, the Hadleys are in the virtual reality created by their children. In the end, Bradbury implies horrifically that Mr. and Mrs. Hadley die for real. Their kids' fantasies have become reality.