Hi we did a similar, but shorter, trip in 2008. Our boys were 5 & 9 & loved it. A few suggestions:-
In Hoi An stay at the beach not in town. We didn't & really regretted it. The beach is lovely & the boys would have welcomed the down time. Whilst hubby & I loved Hoi An we didn't find that there was a lot to offer for the kids
Siem Reap was a big hit but kids find it tiring to spend all day the temples. I'd suggest spending as long there as possible so you can do the temples in the morning then afternoons by the pool. Its worth taking a day trip to Beng Melea as it is quite unspoilt, probably less so now than 4 years ago, & the kids found it quite an adventure to explore.
I wouldn't recommend the boat from PP to SR. It has a bad reputation, I know when we went it was referred to as the "floating coffin". We took the boat from Chau Doc in Vn to PP & that was a great trip. Met some people in SR who we had done that trip with, then they had the done the boat to SR & hated it whilst loved the boat from CD to PP. I am going back this year with the boys & will get the bus.
If you can fit it in do a home stay in the Mekong. It was good fun & showed the kids a completely different way of life. Then if you want to do a boat trip you can take the boat across the border to PP.
Anyway this is what worked for us. Have a great trip. We loved Vietnam & Cambodia.

A couple of comments on claireb's post, one specific and one more general.

1) We were at Beng Melea a year ago and it's still very unspoiled. We hired one of the kids who hang around the entrance to take us around, and while we didn't understand his English very well, we absolutely needed him to guide us in and around, because so much of that temple is in ruins, and you just climb over the rocks, tree roots and pilings to see it. It's fantastic.

2) The first time we took a long trip with our kids (Europe), we planned for downtime at the end, but not in the middle. That was a mistake -- we should have had 2-3 days at the beach in the middle for R&R. The beach in HoiAn is fantastic - you can walk for miles on white sand. We also loved the pool at the Victoria HoiAn. It's only 10 minutes into town by shuttle or taxi.

one small comment, Bang Melea has catwalks built around it now so you can self guide and not be walking all over the carvings. There are a few parts where you can climb around on some fallen stones but following the catwalks keeps you from getting lost.

please don't hire children as "tour guides". They are skipping school and having to turn over your "tips" to the tourist police.

If they were your children would you want them out taking candy from strangers when they're supposed to be in school or otherwise safe from the thousands of pedophiles that come here every day specifically for the purpose of finding vulnerable children?

If every tourist who comes here would stop that, they'd all go back to school and to work at home. It's what you'd want for your children, it's what we should want for them as well.

OK rant over, sorry for the hijack. Enjoy your trip.

Well said offwego!

From your list my favourite places would be Hanoi - loads to see and do (I would include a side trip for a homestay in the Mai Chau valley fopr a day or two. Hue is a great plece to hire some bikes to get around the town and around the tombs etc. Hoi An s worth a day or two and is very quaint, pictureque and compact with some great beaches nearby. Both Hue & Hoi An have some great places to eat. I love the buzz in Phnom Penh, great markets, restaurants. Sights documenting the genocide that took place in the country such as tuol Sleng & the killing fields can be upsetting but are definitely worth visiting.

Sihanoukville, Kampot & Koh Tonsay are all very nice but avoid Tonsay at weekends if you can ( a bit noisy)weekdays it was one of the most chilled out places. No aircon as I recall so it can get hot, but worth it for the fresh fish & crab alone!

I would not take the boat to SR (especially with kids) they are not particularly safe and have been known to sink occasionally. they are usually very overcrowded and if yo get stuck on top do get extremely hot. if you want a boat trip better to get a boat out from SR on the Tonle Sap to sail around some of the smaller, more remote non-touristy villages.

Angkor is spectacular but does get very crowded these days. Parts can be very steep for young children but it will be a huge adventure for them. Do a bit of research beforehand and hire a good guide driver explaining that you have children with you and they should be able to adapt a schedule to suit. (try to get out to some of the outlying temples rather than just the main ones).

Travelling around Cambodia is easy and cheap by minibus. But they do tend to overcrowd them and do not worry about toilet breaks (could be hard on the kids!) - with 4 of you a taxi might be cost efective.

I heard of a family with children in Hanoi and a small boy got so far across the road and ran - was hit by a motor bike. Story may be an urban legend but the traffic is crazy. Hold hands with children while crossing the street.

I'm not sure if the bamboo train at Battangbang is still operating but it would be great for children as part of a tour of the province.

If you go to Banteay Srei (highly recommended) its probably worth going further out to Kbal Spaan. Its a 1500 metre walk up to the shrine but there is an interesting animal place at the bottom with some very weird birds. Its western run and they only do one tour a day at 1 pm from memory. Nice restaurant across the road too.

Take them to Master Feet or similar in Siem Reap for a foot massage. Its only about $6 (plus a tip) for an hour. Good after a day at the temples.

I'd also recommend the boat trip from Chau Doc to Phnom Penh on the Mekong. Do not go to the closest village on Lake Tonle Sap. I can't remember the name but its a real tourist trap. I went to an outer one (near the bird sanctuary I think and it was great. Stopped for lunch at a crocodile farm and saw them feeding tiny crocs.

I'd also recommend Mai Chau for a homestay.

Read up a bit on the history of Cambodia and then decide if you want to take children to the Killing Fields/Toul Sleng. Discuss it with them beforehand as it may be upsetting but on the other hand it will make them appreciate their own good fortune.

If you travel by bus in Cambodia, go with Mekong Express. They have toilets on board.

Enjoy your trip. They are both great countries to visit.

<<<If you go to Banteay Srei (highly recommended) its probably worth going further out to Kbal Spaan. Its a 1500 metre walk up to the shrine but there is an interesting animal place at the bottom with some very weird birds. Its western run and they only do one tour a day at 1 pm from memory. Nice restaurant across the road too.>>>

I'm not sure to what you refer regarding the "tour" -- we went first to Kbaal Spean (before Bantay Srei), climbed the hill ourselves (great hike!), and then did a tour of the carvings and waterfall at the top. There was no "tour" per se. On re-reading, maybe you were referring to the "animal place" -- we didn't see that, don't even know where or what it is. We loved Kbaal Spean, beautiful and peaceful with the added bonus of ancient carvings in the river bed.

<<<We hired one of the kids who hang around the entrance to take us around>>>

FWIW, the "kid" I was referring to was probably around 20, not a child who would otherwise have been in school.

Wow, these are amazingly detailed responses! Thanks everyone for your insights, we really appreciate it and will definitely use them!

Have fun! We go to these spots often with our 9-year old boy. We all have great experiences there! www.cokesmithphototravel.com

The animal sanctuary is at the bottom of the climb up to Kbaal Spean. Its on the RHS as you come down. Thats where the tour is. Sorry if I was a bit vague. However as sf307 says Kbaal Spean is well worth the trip. The animals are a nice add on if you happen to be out there at the right time. I did the trip by tuk tuk but you may prefer a car.

We went by tuktuk too - our preferred
means of travel in Cambodia

Hoi An was a wonderful place and spending time on the Viet family part of the beach really is a treat. I have traveled into Northern Vietnam and there are some beautiful areas, Hai Phong being the most beautiful. Now the facts about family's. I would never dream of taking children to the northern area's. It simply isn't ready for that. First, the bus drivers have complete disregard for life and westerners have lost their lives on mountain roads, and been in serious accidents. There is a government mandate that no westerner is to be physically assaulted, but many Vietnamese still hate westerners, and you'll never know when your family will be the brunt of public humiliation, etc. You may go to an area you hear about, only to find the people are happy to see you suffer and extort money using various tricks. Do Son is a great example. Even Cat Ba has Vietnamese that will act threatening to extort money or resolve problems. Remember that you have no real rights there, and no police to protect you in any way. Vietnam used to have a strong government and many of these issues could have been prevented or resolved. But now, it's official's are more involved with newly won fanatical success and have no real interest in making laws that protect tourists and making sure they are enforced. Nguyễn Tất Thành was a educated, refined and intelligent man and if still alive, I'm sure would have created an National atmosphere that would be true to the principals and humanity he lived by.

Came accross this Travelfish article which might be of interest:

http://www.travelfish.org/feature/150
Some more info via the left sidebar "travel with kids"

PS I have travelled extensively in Vietnam over the last 25 years and have rarely encountered any of experiences to which MiSola refers. Indeed for the most part the Vietnamese are extremely hospitable - not sure that I would be given their recent history and the amount that the people have suffered at the hands of various nations over the last century!