When I was 13, my family went on an organized tour through Yucatan, and I really enjoyed it. I found the sites (Chichen Itza, etc.) really interesting, even as a teen. The last 4 days we spent in Cancun, on the beach, basically. I'm sure you could do it outside of an organized tour as a family as well, but you probably know more about Mexico than I do.

Other than that, I can say that SEA, especially Thailand, is perfectly safe to travel for a family. Don't worry too much about scams. Yes, they can happen, but worst case you burn $30 bucks on an "authentic antique Buddha", made in China. ;) Thailand is very safe, great tourist infrastructure and you can travel it on any budget of your choice, from ultra-cheap to luxurious.

You could spend a few days in BKK, and then go to a quiet-ish family-friendly island. Lots to discover (food, temples, nature), and definitely a different culture. I've been there several times, and never had any health issues with the food. I didn't pay much attention to it, but I'm sure it would be easy enough to find "Western" food in most places, if your son should insist.

Hope this helps a little.