In France, there's a fantastic support network for english speaking mums; it's called MESSAGE Mother's Support. It sounds quasi religious, don't worry, it's not!
Google it, you'll find their website which explains how to join (it costs about 40 quid per year and is worth every penny) and then you'll have access to lots of English-speaking parents who are living in france, have negotiated their way through the education system, health services, financial issues (tax etc)
It can also be a way of meeting Anglo mums in your area
Beyond that, get your french as good as you possibly can, listen to French radio, watch French movies, get your ear tuned to French ASAP
Doin't worry about YOU making mistakes, you will be able to make yourself understood, but if you can't undertsand others, it can feel very isolating
be open minded; so many things about life inj France are so very different, but that doesn't mean worse
in fact, for may things, it means they are better, but sometimes you can lose sight of that
good luck
i am based in paris, so not knowledgeable about brittany, but it is a beautiful area
the people in brittany have a cliched reputation for being a bit cold, but that might be more vis a vis tourists