Your child is the applicant.

You need to use Appendix 1 (VAF4A)

Here's the link to the paper form just for your review and understanding:-

APPENDIX 1 (VAF 4A JULY 2012)- FAMILY SETTLEMENT & FAMILY REUNION


YOU SHOULD COMPLETE THIS FORM IF YOU WISH TO COME TO THE UK AS:
• The adult dependant relative of a person who is present and settled in the UK; or
• The adult dependant relative of a person with limited leave to enter or remain in the UK as a refugee or as the beneficiary of humanitarian
protection; or
• The child of settled parents or with one parent who has limited leave as a partner or parent granted under the Rules in force before
9 July 2012.
Hope that helps.