What moment in the story describes George and Lydia's failure as parents?

Towards the beginning of the story, while Peter and Wendy are enjoying a helicopter trip, Lydia laments about the nursery and tells her husband that she is afraid of the African veldt, which the children have been watching on an everyday basis in their nursery. Bradbury provides a clue that depicts George and Lydia's failure as parents when George mentions that Peter and Wendy threw a temper tantrum last month when he locked the door to the nursery for a few hours. This comment is significant and reveals that George and Lydia bow to their children's demands. The fact that George allows his son and daughter to throw tantrums and is willing to leave the nursery unlocked indicates that he lacks control and authority in his home.
At dinner, Peter and Wendy mention that they are too full to join their parents, because they have been eating hot dogs and ice cream all night. They also lie to their parents about the African veldt, and Wendy purposely deceives her father by quickly changing it before he enters. Allowing Peter and Wendy to consume junk food, skip dinner, and lie to their faces are additional examples that depict their bad parenting skills. Later that night, George admits to his wife that they have failed as parents by telling her:

"We’ve never lifted a hand. They’re insufferable—let’s admit it. They come and go when they like; they treat us as if we were offspring. They’re spoiled and we’re spoiled" (Bradbury, 8).

After Peter and Wendy return from the carnival, they lie to their parents about the African veldt playing on the view screens in their nursery. They say they are not watching Africa, and they actually change what is playing to try to deceive their parents. George, however, finds his chewed wallet in the nursery, and it smells of the African veldt. 
It is after this episode that the parents decide they have failed. George says that children need to stepped on occasionally, but George and Lydia have spoiled their children. George then locks the nursery and says it will stay locked. He also decides to invite Dr. McClean over to determine whether the children are emotionally healthy.
All of this indicates a family in crisis. However, the parents will fail again when they allow the nursery to be unlocked because the children beg them to do so.