Hi there
Thank you
I just came to know from the ircc website that it is required and mandatory by non accompanying Family members.
This section is regarding to family class sponsorship.
It's rare that there will be "non-accompanying family members" that needs to fill military service forms.
e.g. spouse being sponsored by PR/Canadian, their dependents would be children under 22 years old.
Is that your question?
Spouse/common law partner and children under 22 years of age are considered family members.