I don't understand this point...to be honest this point is confusing me:
Minor children before entering Canada
Minor children who want to study for
six months or more must apply for a study permit before they enter Canada. This includes minor children who come with parents who had a study or work permit approved overseas.
You do not need a study permit for a program of
six months or less, but you may still apply for one before entering Canada.
If you are coming to Canada with parents who have a
valid study or work permit, you don’t need to provide a letter of acceptance from a school when you apply for a study permit.