Takemehome
Having read your initial post and being a very frequent visitor to Thailand myself and understanding the culture completely, i really believe that the biggest distraction on the flight was you!
You were right to air your concern when the adult initially went on to the flight deck, but you were told that he was a Captain.....end of story. The kids going up would not have interferred with the landing checks, but you sending the cabin crew to inform of another complaint would have done. Rather than focusing on the job in hand, they spent the last few minutes either vocalising or thinking 'Who the f*** does he think he is, i am the Captain its my decision, i've been made to look a d***head in front of the VP etc etc etc'. To top it all, after admitting you don't know if there is a rule concerning this, you tell a repected member of the airline who comes over to you in the baggage hall and politely talks with you that you think he has behaved irresponsibly!!! I also think it a little unfair on a public forum that you identify him by name and appointment, particularly as you insinuate that he was an idiot. A bit of discretionary editing might be appropriate. You say you live in Bangkok which amazes me even more that you delt with the situation as you did. I hope you dont deal with the Thais you work with like that. Don't be suprised the next time you try to get your cheap flight with NOK the 'computer says noo'.