they
Is this the government? The teachers? The adults? Those adult figures in this child's life who are supposed to protect the child and provide safety? These figures are no more than children themselves, convincing one another of the signs of an attack, providing near useless suggestions such as sitting under a "frail [...] slab of wood." Each and every citizen suffers from the same paralyzing fear of death, and the ever ominous warfare plaguing the world's safety, wellbeing and peace after the world was shattered in WWII.
There is a sharp contrast between the youth and adult approach. The child accepts fate, and understands "reality's gloom" and the dangers that could instantaneously "zoom" through the sky. The adults are unaccepting and instead make every effort to control the situation by feeble attempts to "instruct" faulty principles that will disintegrate the moment the "piercing shriek" sounds.