Hmmmmm that is confusing, I thought you had to fill both but you seem to be right.
This is what the put on country specific checklist 3907e.pdf
2 Additional Dependants/Declaration (IMM 0008DEP) - This form is completed by you, the principal applicant, if you have more than five (5) family members.
Thanks for correcting me
Also this bring me to the question about the language, for a 2 year old who don't speak any language other then Kid language lolz what to put ? I have selected the same Native language as my spouse and put neither on other 2 languages question. That is the right way to do ?