Yes they do change frequently. However “official sources” like embassy websites and the like don’t change as frequently and often give out wrong information. It’s sites like this who are run by people in the know that are probably the best source.
The MFA run embassy websites. Immigration run internal policies. They don’t always see eye to eye or even speak.
For a child under 15 from a visa exempt country don’t really need a visa. Some stay for years without one. They can’t be fined or black listed but would get an overstay stamp on exit.
If you want to school them here then some schools may insist on you exiting to get them off an overstay and return to get them on an education visa.
Looking for visa options now for 2 years down the road is a bit premature. They change fairly frequently and what may be available now perhaps won’t be by then.
Assuming you’re not over 50 then options are limited. Privilege (Elite) if money isn’t an object, DTV for soft power (as you’re not an digital nomad) - if that still exists then or an education visa could be options.
Privilege visa (Elite). Costly but age not an issue.
DTV a five year visa that you can apply for as a digital nomad or through the soft power options of something like Muay Thai or Thai cooking classes or medical appointments.
Education visa. Thai language or Muay Thai. Good for probably max of 2 years.
Find a job here (or start up a company) and get a business visa and work permit.
Or marry a Thai or have a half Thai child. Granted these last two may be extreme, but they work for some.
Why longer than 90 days? That is a long term visa. If a bank won’t open up an account with that then it’s probably because they can’t be arsed to deal with he paperwork- especially if you’re American.