I will accept that going to CM is a squeeze but you can take a 9AM flight and arrive at about 10 and you are driving out of the airport before 11AM, On the return you do not have to leave CM until 7PM and will be in Bangkok airport at 8-8:30 (with a delay). Thay still give you 4+ hours of leeway and no luggage problemfor if you take Thai to and from CM you can check your baggage through to NY from CM and you will have little worries. I just think with the kids and the heat/humidity of BK the kids would like the change especially Lampang. It is not a circus but done so very well. I was unaware that premium economy has gone up from $400 to $600 in the 4 months since our last trip but if you really are concerned about jet lag and cannot extend the trip by 2-3 full days (that's what I would do) it may still be worth considering even though it is $2400 for your family.

If it were me (and, obviously it isn't), I'd opt to spend the time in Bangkok. You don't have a lot of time in Thailand and you will be contending with jet lag, why spend 8 hours or so of your vacation in a van going to/from Hua Hin or to/from Chang Mai? If you had more time, I'd suggest you add a few days somewhere outside of Bangkok. If you choose your hotel well in Bangkok, it will be an oasis in the city. There are lots of wonderful places for spa treatments, great restaurants, etc.

I've been to Hua Hin two or three times. It's a pleasant beach resort area with some very nice accommodations, many with wonderful spas. There are some good restaurants (they don't measure up to Bangkok, IMO) and a little sight seeing you can do. It's pleasant, but not uniquely Thai.

By the way, my first trip to Thailand twenty-some years ago was 9 days in Bangkok. I loved every minute, and immediately planned another trip to Thailand to see more of the country and to spend another week in Bangkok.

You've already gotten a lot of feedback about going for 8 nights, so I won't comment further. I did want to say something about your comment that you could plan a longer trip during the summer, but were concerned about it being rainy season.

I took my daughter to Thailand two years ago for 18 days at the end of July / beginning of August. Quite honestly, I only remember 3 times when it rained. The first time it rained, we were just getting ready to walk to the Skytrain station and decided to take a taxi instead to our destination. The rain stopped before our taxi ride was over. The other two times were up north between Chiang Mai and Chiang Rai; once was when we were staying at the Hmong Lodge and the rain was actually very soothing and the other time was during our boat ride on the Kok River. Besides deciding to take the taxi that one time, the rain didn't affect our trip at all.

It was definitely hot and muggy during the summer, but from what I understand, Thailand is always hot and muggy and those on the east coast are more used to the heat and humidity than those of us on the west coast (especially if you live in a beach city like we do). So, if the weather is what's keeping you from planning a longer trip at a different time of year, I say go in the summer for a longer time.

My two cents, for what it's worth...