Thai Embassy website London has info on the 30 day visa

exemption scheme:

www.thaiembassy.org/london/en/services/7742/84451-Tourist-Visa.html

 

I am looking at travelling to BKK with my son (dual Thai/UK) who has his own Thai

passport. 

I would like to pop down to Sydney, Australia for a few days then return BKK before

leaving for home in UK.

 

Does the visa exemption allow for the re-entry into BKK from Sydney or do I need

a re-entry permit?

You have no visa.
Why would you need a re-entry permit?
When you return from Australia you will get a second visa exempt entry.

Sent from my Nokia 6.1 using Thailand Forum - Thaivisa mobile app

You would receive a new 30 day visa exempt entry each time you enter. There’s no need for a reason-entry permit.

 

Note that airlines sometimes insist that you have a flight out of Thailand within 30 days if travelling without a visa.

Every time you enter you get a 30-day permit. Why it will require re-entry permit. Ice cream brain freeze? You can have reentry permit on Tourist visas.

5 minutes ago, onera1961 said:

Every time you enter you get a 30-day permit. Why it will require re-entry permit. Ice cream brain freeze? You can have reentry permit on Tourist visas.

you can get a re-entry permit on a 30 day VE entry, what if you were travelling via a land border and had used up your 2 VE entries for the year,

11 minutes ago, steve187 said:

you can get a re-entry permit on a 30 day VE entry, what if you were travelling via a land border and had used up your 2 VE entries for the year,

Possibly if you were already on a visa exempt entry or the 30 day extension of one but it that might depend upon the office where you apply for it at.