This thread has links to lot of threads discussing requirements.
Also couple of posts pointing out that if married to mother immigration require extension based on marriage.
Since you are covering much of expenses (school feed, mortgage etc) perhaps they wish to confirm with mother..
In your situation the child is not living with you..
Are you 50+
https://aseannow.com/topic/1327020-extension-of-stay-based-on-having-a-thai-child/