I need some pointers from people knowledgeable about Thai visa rules in these times.

What we (family of 3) desire to do is enter Thailand and get an education visa to stay for up to one year. 

Now the question is: Is that even possible considering our son is 6 years old. And not only that, what is the best way to go about this? Arrange an ED-Visa in advance at the embassy and then enter with COE and Phuket Sandbox model?

Or is it better to enter on a tourist visa or even visa exemption and arrange the education visa after arrival? 

If your son was to enroll in a school he could get a non-ed visa and a one year extension of stay.

One of you could could get a non-o visa for being parent and then a one year extension of stay by showing 500k baht in a Thai bank for 30 days. It may be possible for the other parent to ge a non-o visa but they could not apply for the one year extension.

Getting a non-ed visa at a embassy or official consulate for attending a informal school such as a language school at this time is not possible. It can be arranged at immigration for a additional fee at some schools.