So i contacted cic about adding on our child to the application. This is the email i got from them.
Sir, Madam,
Thank you for contacting Citizenship and Immigration Canada. I am pleased to follow up on your request:
After applying for sponsorship - Parents and Grandparents - Adding a family member (Add-on)
A family member* of the principal applicant could be added at a later date, even if they were listed as non-accompanying dependant in the initial application. However, there is no guarantee that your request to add a family member to an application will be accepted if the final decision has already been made by the office processing the application.
To add a family member to the application, you have to download, fill out, validate and print the following forms** from our website (for more details on these forms, please follow the instructions provided in the Guide) and send them to the Case Processing Centre (CPC) in Mississauga, Ontario:
A new Application to Sponsor, Sponsorship Agreement and Undertaking form (IMM 1344) completed by the sponsor and, if applicable, the co-signer,
(If the application is still at the CPC in Mississauga) A new Generic Application Form for Canada (IMM 0008) without supporting documents,
(If you are adding a dependent child of a dependent child) A new Financial Evaluation form (IMM 1283) with supporting documents,
A new Financial Evaluation for Parents and Grandparents Sponsorship form (IMM 5768) with supporting documents,
and
The add-on request including:
your name,
your client ID number/UCI,
your file number,
a letter of explanation,
a copy of the birth certificate, marriage certificate or proof of common-law relationship, and
if applicable, the proof of payment.
You must write ADD-ON on the forms and on the envelope. If you want proof that your application was received, we suggest that you use registered mail with Canada Post or a courier service such as Purolator, UPS, FedEx, etc.
*A family member is a spouse, common-law partner, dependent child or dependent child of a dependent child.
**If the newly created family member is a child born in Canada, only the add-on request is required.
So it looks like i wont need to send any forms or anything. I will just the add on request with child's birth certificate.