@Henry ********
, we had report of that someone could get Non-O dependent (spouse) on a foreigner who is legally staying Thailand on an extension based on being over 50 from Penang. I think it's worth to call the Thai embassy/consulate in Laos if they issue those visa even not on the website, especially your wife is Lao national.
If they do, both of your wife and child can be dependent on your retirement extension. If not, as Tod says above, get Non-ED and Non-O guardian with 500K in a Thai bank.