@Mar****
then you aren't applying for an extension :(
you need to apply for the Non-O visa FIRST,
and to do that you need 15 days left on your current stamp <- meaning you needed to apply by FRIDAY the 11th to have enough time on amnesty to get thru the "under consideration" period for the Non-O visa.
The only thing you might do is get the letter from your embassy asking for a 30 day extension based on being uable to travel, THEN take that to the immigration office and ask them IF you get that 30 day extension can they then process a 90 day non-Immigrant Type visa based on being the parent of a foreign child in school here by showing the 500K baht in a thai bank account in your name only transferred in from overseas.