Who teaches what
Nidra leads the body scan — toe to crown, calm and level and unhurried — which is yoga nidra, done properly and slowly. Baba Bear breathes in for four and hums on the way out, because a long hum forces a long exhale, and the long exhale is the settling half of the breath. Chief Mindfulness teaches noticing one small thing at a time, straight out of the book Tardy does Mindfulness — raisin and all.
Meditation, not instruction
A child cannot be told to relax any more than they can be told to fall asleep — the telling creates the trying, and the trying is the problem. So these films never instruct. They show someone else breathing slowly, noticing slowly, going quiet slowly, and a child lying in the dark does what children do best, which is join in without being asked.