My two luk krung boys were born outside of Thailand. We went to a Thai consulate and applied for Thai citizenship for them. They were each given Thai passports in about two months. About a year later we moved to Thailand and stayed there for about 12 years. We then relocated back to my home country so they could finish high school and then go on to university. They both have current Thai passports and Thai ID cards. They occasionally go back to Thailand but not often. As they are in their late 30's now, I highly doubt they will ever return to Thailand to work. Holidays, yes but that is about it.
If your Thai wife. ex-wife, girlfriend has all the necessary documentation she probably can go and get the child registered and entered into the tabien bahn but I'm not sure if the child has to be present or not.