Yes....the principal applicant my declare all dependent children accompanying and non-accompanying in IMM5406.
SECTION B
Write the personal details for your children. It is very important that you list all of your children (even if they are already permanent residents or citizens of Canada). This includes:
married children,
adopted children,
children of your spouse(step-children) or common-law partner,
any of your children who have been adopted by others,
any of your children who are in the custody of an ex-spouse, former common-law partner or other guardian.
You must answer all questions. If any sections do not apply to you, answer “N/A