 Why are the grey helmets necessary?
"Full psi precautions?" asked Dorffman. The first was from Roberts Bros., announcing another shift of deadline on the book, and demanding the galley proofs two weeks earlier than scheduled. And the more they struggled, the thicker and more impenetrable the bramble bush became— But now David Lessing had discovered a pathway through that jungle, a theory to work by— At his elbow the intercom buzzed. "In fact, you can't really be certain that your instruments are measuring the children at all. Just as the ability to think logically in a crisis instead of giving way to panic is a differentiating quality." For one thing, it seemed to be immensely more powerful and active in infants and children than in adults.
 The helmets block external psionic forces.
 The helmets block external psionic forces.  The helmets improve the reception of external psionic forces.  The helmets are for safety, as the children are heavily medicated and at high risk for falling.  The helmets amplify the childrens' psychic abilities.