Remember that in this terrifying vision of a dystopian society, the big equalling factor is that everyone by law is required to be the same as everyone else - no one is allowed to be better or more intelligent. Thus, when the narrator tells us about Harrison, Hazel and George's son, being taken away, he then goes on to explain why his parents are unable to think about it and get upset about it too much:
It was tragic, all right, but George and Hazel couldn't think about it very hard. Hazel had a perfectly average intelligence, which meant she couldn't think about anything except in short bursts. And George, while his intelligence was way above normal, had a little mental handicap radio in his ear.
This handicap, the narrator goes on to inform us, would send out a sharp noise every twenty seconds or so, meaning that George is reduced to "average" intelligence. It is because of this that Harrison's parents are unable to think about him and get upset about what has happened to their son.