I used chatgpt to write one. Just a few lines with your detail, your child's details, relationship and you'll support him financially in Thailand. Doesn't have to be long.
Apply for dtv- dependant. It's relatively easy. You just need to provide your bank statement with a sponsor letter stating you'll be financially responsible for them. Much easier to get than the main applicant
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.