Bunk beds are meant to be taken fully apart, and they should be, both to fit through doors and to reassemble safely. The keys are labeling every part and never losing the specific bolts that hold a child up in the air.
Pro tip: Tape each labeled hardware bag directly to the matching rail so bolts never get separated from their part.
Watch out: Do not substitute or skip any bunk-bed bolts; the hardware is engineered to hold a person off the ground and missing fasteners make the bed unsafe.