As many of you know, I have been living in Alsace for 15 years. I am happy here, and speak French (but not Alsacian) and have learned German.
First of all, any move is a risk. When you move to another country the risk can be overwhelming, and you should try to prepare for it in advance even if the move is of your choice. That includes language classes, reading about the everyday culture (yes even from books like Peter Mayne's much copied Provence books), and taking a really long hard and often distressing look at yourself .. what you need to have to make life bearable, and what you can do without. Any problems in relationships don't go away just because you change country!! They often get worse.
You need to consider health, employment and insurance issues. And then your children's needs as regards schooling, leisure activities and so on.
AND TALK ABOUT THEM, and KEEP TALKING. I have seen so many families in turmoil because they didn't prepare adequately, and didn't realise that they would be vulnerable in areas in which they felt so confident at home .... ordering a pint, filling in a form, car servicing ...
You should consider NOT burning your bridges at home. Keep your UK bank accounts, rent rather than buy immediately, and if you really find yourselves throughly miserable and NOTHING can help you over the bad times (and there will be many ... sorry been there, and got the t shirt!), then go back to the UK if you feel that's the only place for you, and carry on living without a feeling of failure, more that you tried something interesting, and having tried it fairly you've decided to come back to the UK.
You will discover a great deal about yourself - not all of it good - and having an open mind (they do things differently here ... not they do it wrong) will help you cope with all the facets of a new life.
You can expect to feel a bit blue once the honeymoon phase has worn off, and only once you've been living abroad for a good year or so, will you feel that you know a bit more about what's coming next in your new life of discovery, having been through the seasons once.
GOOD LUCK - and BE KIND TO YOURSELF.