To be released from society means to die or to kill yourself.
The children are corrected and scolded for telling some of their playmates that they should be released. It was taken badly by the adults.
The adults know what the term "release" means, but the children do not know. The youngsters do not know what it means, but Jonas finds out what it means when he is learning the job of "keeper of memories". He witnesses his father "releasing" one of two twins. Jonas of course is mortified.
Later in the novel we learn that the current "keeper of memories" intended to pass the job on to his own son, but that son insisted upon being released before the job training was completed.
"What a world, what a world"
Being "released" means being euthanized, or death. One way the society in which Jonas lives maintains their utopian status is by releasing anyone who might present a problem or complication. The elderly are released, thereby preventing the emotional, societal and fiscal problems associated with illness. Similarly, the weakest of infants are released when it becomes apparent that their health is going to be a continued problem. Additionally, members who do not conform to the rules and expectations of the community are released, thereby preventing the complications that occur when people have differences of opinion or try to express individuality.
To remove them from the community. Later on you would find out.it meant killing them.
IT MEANS THAT THEY ARE GOING TO KILL THEM