It's on one of the sponsor's forms -
IMM 1344A - and the instructions for how to designated A, B, or C are found in the
Sponsor's Guide,
page 6 of 33.
Dependent children
Your child or a child of the person you are sponsoring will be considered a dependent child if that child
A. is under the age of 22 and not married or in a common-law relationship; or
B. married or entered into a common-law relationship before the age 22 and, since becoming a spouse or a common-law partner, has
• been continuously enrolled and in attendance as a full-time student in a post secondary
institution accredited by the relevant government authority and
• depended substantially on the financial support of a parent; or
is 22 years of age or older and, since before the age of 22, has
• been continuously enrolled and in attendance as a full-time student in a post secondary
institution accredited by the relevant government authority and
• depended substantially on the financial support of a parent; or
C. is 22 years of age or older, has depended substantially on the financial support of a parent since
before the age of 22 and is unable to provide for him/herself due to a medical condition.