I envy you, OP, we have recently come back to the UK after 10 years on the road with our family. We loved every minute of it and are reallly missing the sunshine and the adventures.
Any regrets? Only that my kids do not seem very close to their cousins as they have only seen each other once or twice a year while growing up, but hopefully that will change as they spend their teenage years together.
And I wish we could have got the PILs set up with a really simple laptop so they could Skype us - talking on the phone was never good with 2 and 4 year olds, but it got better over the years.
There are stresses with the move, and getting set up abroad with phones, broadband, cars, houses, furniture, Social Security numbers etc, but I have found coming home and doing all these things have been no less stressful. You know you just have to get through it.
You will find wherever you go there is an expat community, and they will be most welcoming and supportive - they've all been through it.
Are you getting a familiarisation visit? If so, I would try and make contact with a couple of families at your destination with similar aged kids, and arrange to meet them on your visit. With a few regular exchanges of emails you'll have a better idea of what to expect. We did this for a few families - one girl even came into school for a day with my DD and that really helped her look forward to the move. Even if you don't visit, this and the other websites above will get you into a network where you can find someone with similar age kids and start PM'ing.
Try not to worry about DD1 too much - acknowledge her feelings and reassure her, but know that kids are amazingly adaptable and resilient. It's us mums that suddenly sit back one day and think - 'Phew, I did it - all unpacked, DH in new job, kids happy at school - what do I do now?' That's usually the point at which I had a day of crying - mixture of relief, exhaustion, missing old friends, and wondering what to do with my life.
I'm still wondering. But I wouldn't have changed a thing about the last 10 years 