@Farhana *******
. The conditions in place at present would not allow your son to come to Thailand, as he is now too old to be classed as a "child", way too young for any "retirement" visa, which leaves work permit, if he can secure short-term employment, education visa if he enrols in a university course (possibly his best option, he should enquire with universities to ascertain if there are any short term courses which are eligibles), ED visa is not yet applicable for language schools. As there are no tourist visas, the only other option is an Elite Visa, but that's an expensive venture, although if you do have the funds, it will take care of his visa requirements for the next five years, if he intends visiting you in Thailand during University breaks in Australia.