I was looking at one of the Thai Immigration sites and saw that 500k was required in the bank for an extension of stay. Did they raise the amount from 400k? https://www.immigration.go.th/?p=14695

No.

400k on day of application for Non O marriage and .....

400k seasoned for 2 months prior to application for extension 

500K baht is the amount required for a Non-O 90 day visa or a yearly extension of stay based on you are raising a foreign child here who is enrolled in school on an education visa.
For the year extension the 500K baht seasoning is 30 days for the first year and 3 months for every year after that   

The financial requirements for a Non-O 90 day visa or yearly extension of stay based on marriage to a thai would be 400K baht  

For the year extension the 400K baht seasoning is 2 months before you apply for the extension

I see my error, thanks

Are you talking about being parent to a Thai child, or about a foreign child attended International school in Thailand?

 

For the first the needed bank deposit is 400k baht, for the latter you need 500k baht.

 

More useful information about guardian of a foreign minor (not more than 20 years old) studying in Thailand (copy link):
https://www.krabiinternationalschool.com/visa-information/

I did this 2 years ago—400k in the bank, which was removed a day later. No seasoning. I was and am supporting a Thai child under 20.

 

6 minutes ago, Gobbler said:

I did this 2 years ago—400k in the bank, which was removed a day later. No seasoning. I was and am supporting a Thai child under 20.

 

The OP is asking about non Thai children.

Off topic posts removed. Thread is regarding Non Thai children..