What's the climax of "The Veldt"?

"The Veldt" is a parental horror story that ends, ironically, in horror dealt to the parents (ironically, because they are horrified by what they witness in the nursery not knowing that the nursery will give them their own horrifying end). The climax of this horror story wrapped in convenience and luxury is when the fates of the family members are irreversibly sealed behind the slammed door of the nursery: the children go their way to tea parties among lions and the parents go their way to the feast of lions.

As the emotional impact of the story mounts with every warning word George utters, the children become more and more assertive and more and more quietly aggressive. Their aggression builds as a quiet thunder because they know they have the ingenuity and power on their side: ingenuity, because they can manipulate the parents to their own will through wiles based on their parents' love and protectiveness; power, because they possess the mental keys to access the nursery's demonstrated ability to change reality; the nursery's power has been demonstrated in George's blood stained wallet and in Lydia's "bloody scarf":

"Hello." [McClean] bent and picked up a bloody scarf. "This yours?"
   "No." George Hadley's face was rigid. "It belongs to Lydia."

The climax to this mounting emotional tension and conflict comes when the door slams behind George and Lydia who are then trapped in the nursery behind a locked door and surrounded by lions: "The lions on three sides of them, in the yellow veldt grass, ... roaring in their throats." Leading up to this moment, Wendy and Peter have devised a plan. They call out to their mother and father as though in danger, "'Daddy,  Mommy, come quick - quick!'" With the children "nowhere in sight," George and Lydia naturally rush to the nursery, throwing open the door and dashing inside. Africa is in place. The lions are there, "waiting." The door slams behind them. The climax is ushered in to the screams of both as George yells "Open the door!" Peter tries one cold, chilling time to negotiate a victory for themselves and the nursery: "Don't let them switch off the nursery ...." George replies, "Now, don't be ridiculous...." And then, as the climax, the parents heard the waiting lions:

   And then they heard the sounds.
   The lions on three sides of them, in  the yellow veldt grass, ...rumbling and roaring....

The climactic fates of George and Lydia are sealed. The story resolves despite them. They have no more decisions to make. After this climax comes the falling action and the resolution wherein Wendy offers tea to McClean in the silence replacing her parents screams, and the lions feed quietly under "shady trees" in the background.

At a distance Mr. McClean saw the lions ... quieting down to feed in silence under the shady trees.
     [McClean] squinted at the lions with his hand tip to his eyes.
     Now the lions were done feeding. They moved to the water hole to drink.
     A shadow flickered over Mr. McClean's hot face. Many shadows flickered. The vultures were dropping down the blazing sky.
     "A cup of tea?" asked Wendy in the silence.