2 days-1 night in Along only; one get bored of limepeaks after 2 days + a 7-year old ends up "turning around in circles" on a boat.

NO night train Hanoi-Sapa ; 10 hours to Lao Cai + 1 hours bus LC-Sapa (at 5h30 !). Take the espress bus DIRECT Hanoi-Sapa, 5 hours on the new expressway (depart Hanoi 7h30)

NO TIME for Phong Nha. FLIGHT Hanoi-Hue

CAR Hue-Danang for a superb day hue-Lang Co Laguna-Pass of the Clouds-Danang Cham Museum-Marble Mountain-Hoi An

2 days in the Mekong Delta Saigon-Cai Be-Can Tho- Cai Rang Floating Market-Saigon

Hey Maury,

I was in Vietnam a few moths ago and did the later half of the trip you are planning. Below are a few observations I had for myself at the end maybe some might help you plan.

Hanoi - The art scene here is great with some really interesting galleries. Ho Chi Minh’s Tomb is very interesting and I would suggest including this. Hanoi Hotel is also very interesting but probably doesn’t reflect recent history fully.
Hue - I found to be a very relaxed city compared to ours in Vietnam. 2 days is probably enough but there are some areas around which may be of interest.
Ha Long Bay - Spectacular. Work hard to find a way to see the bay away from the crowds so you can relax and take it all in. The floating villages are extremely interesting.

After leaving the places I wish I had gone or know I will go next time are the following

My Lai/Quang Ngai
Sapa/Fanispan

Random points. If you are planning on renting a motorbike etc make sure it is included in your insurance. If you want an idea what the country is like and pretty much follows your route then I suggest watching an episode from a British show called ‘Top Gear’ the Vietnam Special.

Enjoy!

If you go to the Morning Alms giving ceremony, please be respectful. This is not a human zoo, but a religious ceremony and some visitors behave like they are in a zoo, which is really disgusting (I am not at all accusing you of that). This page offers quite good advice on the "etiquette" http://www.visit-laos.com/luang-prabang/alms-giving-ceremony.htm#.

Luang Prabang has great markets, for goods and for food. Its also a great place just to walk around, get lost, discover small temples, venture into small villages, have a coffee and people watch, play petanque with some locals etc. Its also fun to rent a bicycle and to discover the surrounding areas by bike.

I went to Muang Sing about 2 years ago, IMO it has gone down hill from my previous visit about 14 years ago. There are less tourists going there now, more chinese influence, less interest the market has moved out of the centre and there are very few tribal people there now. The tourist office (where treks can be arranged) is closed all weekend. Several people I met there were leaving early as not much to do. Even hiring a bike was very hard work, I only found one place and that was expensive. Its also not so friendly anymore. If I had my time again I would go to Phonsali. Buses are not so good either, before you could get a large coach all the way to Luang Prabang, now you have to take minibus to Luang Namtha and from there either a minivan or very old bus. So it will take at least 10 hours by bus. To Nong Khiaw you have to take a bus to Pak Mong and then take a bus or songthaew from there, will take about 7 hours from L Namtha and about 9 hours from Muang Sing.

We're not going to Hanoi. Will probably try Chiang Mai.

I traveled in Vietnam, South to North, with 3 children in July. They were 11, 11 and 6. We spent 5 nights in Hoi An and 2 in Hue. I think 5 nights in Hoi An is too much, but we wanted to spend some time at the beach with the kids. 4 nights (counting two afternoons at the beach) would have been more than enough. In these days, we spent one in Tra Que doing a cooking class with Baby Mustard (that I highly recommend). It was one of our Vietnam highlights. Nguyet was amazing with the kids. They loved their day. If you don't count the beach and Tra Que village, 2 days is enough in Hoi An. Two full days in Hue was necessary, and they were two very full days. The first day, we visited the Imperial city on our own in the morning. Then, returned to our hotel for a swim in the pool (it was one of the hottest days), then we did a 4 hour street food tour on cyclos. It was expensive for 5 pax but another highlight. It combined food tasting in Hue + trying out the cyclos. On the second day, we had a French guide and driver pick us up in the morning. I think it was the best way to visit the Emperors' tombs (we visited 3) and finished at the Thien Mu pagoda and returned to our hotel on a dragon boat. We had an evening flight to Hanoi. I have to add that the travel from a Hoi An to Hue was incredible. We had a (very interesting) driver who drove us via the beautiful Hai Van Pass. We stopped for lunch at Lang Co beach, but what the kids really liked was Marble Mountains. The driver told us he would wait for us at the bottom in an hour, but we got lost exploring and it took us two hours to get back to the car. One hour is not enough for Marble Mountains (in my opinion). The kids would have spent the whole day...

Here are some photos:
http://image.vietnamnews.vn/uploadvnnews/Storage/Images/2015/10/20/07a.jpg
http://img.cdn2.vietnamnet.vn/Images/english/2017/08/08/14/20170808144312-1.jpg
http://imgs.baobacgiang.com.vn/2017/03/08/09/20170308090610-dl.jpg
https://traveldanang.org/wp-content/uploads/cua-dai-beach-2.jpg.
https://media.istockphoto.com/photos/erosion-climate-change-worldwide-warming-vietnam-picture-id517371408

Imagine if you booked a beach holiday and arrived to find this...

Anywhere you go at that period, it will be hot. The less hot would be the north of Vietnam, where you have mountains 1500-3000 m high, with 6-8 days in the Center (Hue and Hoi An, the latter for beach time). NOT thz south, which is monsoon time. With 2 months, I would do the north of Vietnam and the north of Laos (Luang Prabang and around)