For a 30 day extension in Chiang Mai you can go to either the main immigration office by the airport or to the satellite office located in Central Festival Mall.
You need to have a TM 30 receipt showing you're registered as staying in Chiang Mai.
In Chiang Mai you can apply for an extension when you have 45 days or less left on your current stamp
This is a general list of what documentation an immigration office is likely to require to get a year extension based on retirement, it is NOT office specific, which is why I said go to your office and talk to them about it 🙂 and get the hand out listing the requirements at that office
I still think you're way better off doing it all where the current extension was issued rather than cancelling the current employment extension and then going to C/W wanting to get a new year extension based on retirement.
So GO talk to your immigration office (where you live/got the extension/do 90 day reports) and see what they say about cancelling your current employment extension a couple weeks early then immediately applying for the year extension based on retirement
As Gary pointed out you will have to have the 800K baht funds seasoned in a thai bank account in your name only for 2 months before you apply for the yearly extension. You'll need the 'standard' bank letter, the 3 month printed detail transaction report (to show the 800k was in the whole 2 months before you apply). You have to update your bank book the date you apply for the extension along with providing them all the documentation that office typically requires for a year retirement extension
the 800K only has to be banked for 2 months so if your immigration office said it's 3 they're yanking your chain. The bank can print a 3 month statement but that has nothing to do with the amount of time you really need to season the funds
I would say your best bet would be to cancel the extension of stay based on employment at the immigration office where it was issued and immediately apply for a new yearly extensional stay based on retirement by meeting the financial requirements.
Then move to Bangkok
Once you do, file a new TM 30, start doing your 90 day reporting at Chaengwattana and the following year apply for your extension thru that office after you have a year 'track record' under your belt.
Okay keep in mind that just because there is no overstay fine for children under 15 and no banning for children under 18 that is not the same as saying they "don't need a visa to be here"
There was just a recent case where a foreigner was flying back in to thailand on a valid visa and their young (8 y/o) child was coming back in with them on a 'free stamp' (visa exempt entry).
They were pulled aside by passport control questioned as to why the child didn't have a valid visa AND the child only got into the country because the parent was able to contact their employer who assured immigrations that they would apply for a "piggy back" Non-O visa for the child (family member of a foreigner who legally works here)..
So whether you can or can't get a child in free stamp if you're on a Non-O visa seems to come down to the officer you're in front of at passport control
remember once a child hits 15 and overstays while they still can't be banned (that happens only when they turn 18) they can be fined for overstay @ 500 baht a day like everyone else
they could come in get the 60 day stamp, then take the 30 day extension at the immigration office, after that they'd have to exit/re-enter to get a new 60 day entry, take the 30 day extension, etc
had to be a while back seeing as they're not even asking for the print out or the QR code anymore at airports. They can see when they scan your passport if you filed a TDAC or not