visa-exempt entries are for tourists so if you are here to visit your son you need to get Non O visa based on visiting family for more than 60 days. You will get a 90 day entry when you arrive
My friend did it last week and it took 5 working days. If you're not sure ask on here or PM me. I've done 3 in 3 years due to circumstances beyond my control.
2) Visa run (go to another country and apply for a visa that is not available within Thailand) border bounce ( go to a nearby land border and re-enter visa-exempt) Always best to do this with an organised travel company as they have agreements in place for a trouble-free re-entry.
Only untaxed earning that you bring in to Thailand are liable for tax. If funds brought in to Thailand are already taxed in country that has a double taxation agreement then there is no tax liability.