To determine whether a minor child attending school in Canada requires a study permit, it is best to read through the IRCC information. [See IRCC: Study permit guidelines, minor children] You may want to consult a registered Canadian Immigration Consultant or lawyer if you are unsure.
The definition of minor child depends on in which province the child will study.
You are considered a minor if you are less than 18 years of age in: Alberta, Manitoba, Ontario, Prince Edward Island, Quebec and Saskatchewan.
You are considered a minor if you are less than 19 years of age in: British Columbia, New Brunswick, Newfoundland & Labrador, Northwest Territories, Nova Scotia, Nunavut and Yukon.