If you pay the 1900 Baht for extend, you will get a stamp like this for 30 days more. You can extend it at any time, not need to wait for the last minute. Very easy. βΊοΈπ
Go to the immigration you and your kids, and apply for the ED, and take all paperwork from school, if not enough the immigration will say what you need more. So not stress. And like other told, your kids get a 90 days.
The school not do anything, just provide paperwork, so all about ED visa is a business with you and immigration only.
All will be fine. π
Btw remember some pictures of the kids, (little bit more big than a passport picture) and a pen. (Many times I try not have a pen there when get a form from immigration. ποΈ π