Yes and no.
I think that is exactly where I got confused when I filled out the form the first time. I did
not include my citizen kid in Section B, because it says "children who are PRs or citizens are NOT included on that form". Then my application got
returned. Reason: "Children not listed and/or listed incorrectly" in Additional Family Information (IMM 5406).
I think what they mean is: Do not fill out this form FOR your citizen kid (as a secondary applicant or whatever, because the kid is already a citizen and doesn't need to apply for permanent residency).
BUT: If you are the principal applicant you have to list your citizen kid in Section B.
See here
https://www.canada.ca/en/immigration-refugees-citizenship/services/application/application-forms-guides/imm5406.html
"How to download and fill out the form (paper applications)"
Section B