These "policies" are part of the general policies that any passenger is required to know and verify on their own regarding international travel. This is governed by Canadian and Foreign entry and exit regulations, for example from the Government of Canada travel webpage:

"Children and travel

Any adult travelling with children may be required to show evidence of parental/custodial and/or access rights, or to provide evidence that he or she has the consent of the parents, legal guardian, and/or the court to travel with the children.
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