In addition to the required documents for a visitor visa, you must include the following documents:
A copy of the child’s birth certificate
A letter of authorization, preferably in English or French, signed by their parent(s) or legal guardian.
The letter of authorization should include:
the parents’, or legal guardian’s, address(es) and telephone number(s), and
the name, address and telephone number of the custodian (the adult who will be responsible for the child while in Canada).
For more information, see Minor children travelling to Canada.