I believe you would need to send the financial capacity document since you are sponsoring a child based on this page: https://www.quebec.ca/en/immigration/sponsor-family-member/sponsoring-spouse-conjugal-partner/submitting-undertaking-applicationHow about the financial capacity?
Regarding financial capacity Immigration-Quebec_A0535F:
I'm sponsoring my spouse and kid, do I need to submit the above-mentioned financial capacity form as a Canadian citizen. Please let me know. Thank you
"Evaluation of financial capacity
You must complete this form only if your husband or wife, de facto spouse or conjugal partner has a dependent child. "