If you change to non b,as a volunteer then I believe your son would change to non o, as family dependent. I would wait for a more experienced response.
I encountered this chain of events personally. I obtained a visa via Lao but after getting the work permit and extension I changed schools. I changed my work permit but foolishly believed my visa was still valid for 4 months. Upon attempting to renew my visa siracha immigration advised that my visa has expired when I left my previous job. My visa was cancelled immediately and kicked out of Thailand and requested a 20,000 overstay payment. This was a few years ago now.