Why does John have so much trouble dealing with the children and the Head Nurse?

John is experiencing a good deal of grief about his mother dying and can't understand why children are being allowed to intrude on the experience.
They pop up around Linda's bed as John sits with her. They make rude comments about her, because they have never seen anyone fat or old or with bad teeth.
John doesn't know about the death-conditioning children in the World State undergo to make dying seem pleasant and natural to them. He gets angry at them for clustering around Linda's bed. He even lifts one child up and slaps him, sending him off "howling."
This noise attracts the Head Nurse, who asks what is going on. John says to her:

"Well then, keep them away from this bed." The Savage’s voice was trembling with indignation. "What are these filthy little brats doing here at all?"

The nurse, however, is far more concerned that the children be properly conditioned than with Linda being allowed to die in peace or John's grief. Rather than speak to the children, she threatens to have John thrown out. Essentially, John has difficulties because he doesn't understand the norms of this culture.