What visa options are available for British children accompanying parents on an Ed visa in Thailand?

You cannot get Non-O dependents for your children when you are on Non-ED with private Thai language schools. Only possible if you are studying for degrees at a real university.

If you want them to be in Thailand legally, you need to get them a visa. If they go to schools in Thailand, they can apply for Non-ED on their own.

On the other hand, many parents let their children overstay because:

- under 15 yo wouldn't be fined for overstaying

- under 18 yo wouldn't be blacklisted for overstaying

Just penalties are waived for minors, but still overstaying is illegal and they would get overstay stamps on their passports. And once they are on overstaying, it means they are staying in Thailand illegally, and they cannot change their status to legal ones inside Thailand.