Rain Walker there is no overstay for children under 15years old. So your child can just stay in Thailand. Take the Ed visa first. While thinking of what other visas to apply for. I got the elite for myself and my husband after Ed visa. No issues with both my child leaving and re entering Thailand. They will just give a chop when you leave that stares children below 15 of age overstay is waived.
Should have started off saying your son has Thai nationality. Because just being born in Thailand does not equate to joining the Thai army. Thanks for starting unnecessary conflicts in the comments.
Try purchasing a small condo since he is able to retire. Assume he's not of age for the retirement visa. If he's able to pay can consider the elite visa. Cheaper alt will be to get the non o