I've crossed that border several times with no problem. Once I stayed for 7 days, I was charged a fee for a short stay. 2 weeks later I entered the Friday morning and returned to Thailand the Friday afternoon no fee and no problem.
Print everything out and make sure you can access any or all of your information from your phone. You can take your laptop with you and leave it at security. If you need anything on there they will allow you to fetch it and access the information. I had all my documents and they asked me to log into my bank account to show them as they were not familiar with the bank in my country (I'm South African) Chances are you go there loaded with everything and you get the easiest IO Interview you 😂 But I would rather be prepared.
Unfortunately he will have to start the process from scratch. I had my interview in Laos I forgot to ask a question that I considered important and went back to ask if I could see the Immigration Officer again. I was told NO in no uncertain terms and shown the door. This was basically 2 mins after I just spoke to this person. So to answer your question if he can just go that would be a big NO. I needed a document notarized by my country and they gave me a 6 month visa instead and told me to reapply when my docs are sorted 😂 Oh and no refund of my fees.
With all the madness in this world and so much child trafficking I would suggest getting a letter of authority from the parents showing you have permission for them to travel with you. Might not be necessary but I do believe it could be a saving grace if just one person decides to question.
I found several places selling open water wetsuits in Hua Hin:
* Hua Hin Divers is 6.5 km away. It has a 4.4 star rating on Google Maps.
* Duotone Kiteboarding Club - Kiteschool Thailand is 7.7 km away. It has a 4.9 star rating on Google Maps. It is open from Monday to Sunday from 9:00 AM to 6:00 PM.
* Efoil Thailand - Hua Hin is 7.9 km away. It has a 4.7 star rating on Google Maps. It is open from Monday to Sunday from 9:00 AM to 6:00 PM.
* Surfspot Huahin is 8.1 km away. It has a 4.4 star rating on Google Maps. It is open from Monday, Tuesday, Thursday, Friday, Saturday, and Sunday from 10:00 AM to 5:00 PM.
* KBA Kiteboarding Asia HuaHin
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- Kitesurf, Wingfoil and Efoil Center is 8.2 km away. It has a 4.7 star rating on Google Maps. It is open from Monday to Sunday from 9:00 AM to 6:00 PM.
I would rather be safe at a cost of 1900 Baht than sorry as I was not built for prison 🤣 Take the risk get one immigration officer in a bad mood because he had to deal with another farang and it's game over. Do the right thing even if it costs a little more.