Do My Children Need to Submit a 90 Day Report If They Are Leaving Thailand for Vietnam?

Okay, keep in mind the way the 90 day reporting works IS

IF you are in thailand on the date your 90 day report is due you are obligated to report. Period, end of story, there is no grace period. It is what it is

IF you leave the country BEFORE your 90 day due date you do NOT need to report and your next 90 day report will be 89 days from the date you stamp back into the country (they count the day you stamp in as day 1).

There is a fair chance that IF you leave without doing a 90 day report that is due the next time you go to do one they will see you were here 90 days but didn't file one and fine you 2000baht for failure to file.

That's how it really works.

The 90 day report is for reporting the fact that you are in the country for 90 days. If you're not in the country for 90 days then you don't report that you are, because you're not. :)

No. But don't forget to do the TM30 when you return.