In the Halo universe, we know that:
SPARTAN-II candidates were abducted as children at the age of 5 and raised in a military lifestyle, to know only war, and operated on, for armor augmentations.
How did the ONI control them and keep them in line when first abducted? At that age the kids would royally freak out when realizing where they were later, no longer being home or with family. Cooperation would be a logistical nightmare to obtain.
Putting them under and keeping them under would have been detrimental to their physical health and to the whole point of the program Halsey developed.