I've booked a trip to the USA for myself and my child aged 4.

I intend my daughter to exit Thailand using her Thai passport (with departure card), and thereafter to use her U.K passport to enter USA with ESTA, later returning to Thailand using her Thai passport again (with entry card).

Do I need any papers to get her out of the country? , i.e. birth certificate, book house, marriage papers etc.

I'm married to a Thai lady.

Do I need custody papers?

You probably won't need it, but yes a letter from the mum with contact details and your travel dates. Always useful to carry copies of house registration, birth certificate etc just in case you lose the passports and need new ones anyway. Immigtation shouldn't need them for departure having said that.

OP I can't answer you, hopefully one of the uber-mods will advise shortly. Thank you for posting the question.

a letter from the mum with contact details and your travel dates.

Should this be accompanied by a signed copy of her ID card? Should there be an English version for the return journey?

As the US seems an unusual destination for father and daughter leaving living mother behind, it might be handy to have a document explaining why the OP's going to the US. However, I think it unlikely to be needed, just as it is unlikely that you will be involved in a traffic accident in the US.

Don't forget to present the UK passport to check-in when leaving Thailand; foul-ups have happened when someone has initially presented the wrong passport on a flight to the US. A rejection message does not always explain the problem. I trust the OP's flight to the US is booked citing her UK passport.

Thanks All

I completely forgot about the check-in at BKK !

Our passports now have to be pre-cleared by US immigration at Abu Dhabi, and could take a while.

I arrive at AUH at 23.55 and have been told that US immigration don't work at night, so I don't know how that's going to work.

a letter from the mum with contact details and your travel dates.

Should this be accompanied by a signed copy of her ID card? Should there be an English version for the return journey?

As the US seems an unusual destination for father and daughter leaving living mother behind, it might be handy to have a document explaining why the OP's going .

Might be an idea to have a copy of the mums ID card. As said, all as a precaution rather than anything I've ever needed. I've flown with one of my daughters a couple of times and was never asked.