@Ivo **********
you are incorrrect. If you have a child with a thai woman out of wedlock (when you're not married) you do NOT get any legal parental rights and cannot use the child as a means to get a long term extension of stay inside the country.
It doesn't matter if you have your name on the birth certificate OR if you get a passport from your country for your half thai child, according to thai law you as the father have no legal parental rights. To do this you go thru family court and get granted legal parental rights OR depending on the age of the child you can sometimes take the mother, child and yourself to the local Amphur and they will grant parental rights BUT the child usually has to be at least 6 or sometimes 8 y/o to do that (it varies by Amphur). Those are your choices.