Dear Immigration official of the Royal Thai Government Please be informed that as of April 10, 2023, the U.S. Embassy in Bangkok and the Consulate General in Chiang Mai no longer issue passport linkage letters. For purposes of transferring visas for cancelled U.S. passports to new U.S. passports, please refer to the passports themselves.
AFTER u have the 400,000 in the bank fly out or land border and return on a 30 day visa exempt entry>
day after you arrive go to immigration with ur bank book and child's BC and tell them you want a non o conversion . They will tell you what else you need, the visa is 2,000 baht, Than after 60 days apply for the 1 year extension.