Can I obtain a one-year multi-entry Non-O visa outside Thailand based on my marriage to a Thai citizen and my child?

Keep in mind IF you go to another country and get that year-long, multi-entry Non-O visa from a thai consulate it means you only get stamped in for 90 days at a time and have to exit/re-enter to get a new 90 day entry stamp for the validity of the visa.

As Robert pointed out, seeing as you do meet the financial requirements why not go to your immigration office and see if you can get first an in country 90 day Non-O visa based on marriage and then a year extension after that. That way you don't have to leave the country every 90 days

I’ve done the same visa in Ho Chi Min City as well as Abu Dhabi and Dubai.

HCMC used to do the 1year multiple entry visa without the financial requirements.

Depending on your current stay inside Thailand and with 400.000 Thb in your bank account you can apply for:

Conversion into the Non Immigrant O visa based on marriage

Extension of Stay based on marriage and when that is stamped into the passport the Multiple Re-Entry Permit to travel during the year.

OR

Visit the Thai Consulate in HCMC Vietnam or Savannakhet Laos who issue the 1 year Multiple entry Non Immigrant O visa which gives you 90 days of stay on each entry.

"the right amount of money in my bank account" ? What do you mean?