This is the email from CO :
"In order to progress your application, the following information is required. You must provide me this information within 28 days after the date of this letter.
1. Evidence that any child under the age of 18 years who is also named as an applicant, may travel with you.
For any child under the age of 18 who would not be travelling with both parents or legal guardians if this visa is granted, provide evidence of custody or responsibility for the child (such as a court order), and the right to determine where they should live.
I note that the father of the child has also a visitation right over the child, please submit Form 1229 signed by the father and the Certified ID of the Father.