Do your children speak any French already? Because I know everyone says "oh, children are like sponges, they'll just pick it up!" But that's not always true, especially the older they get, and I think your 11 year old in particular might have a difficult year at school unless he's already a pretty fluent French speaker. And even then, the French schooling system is, I'm told, quite different to the UK one. Do you know how and when to register them? Do you (does he...) know where he wants to move to and what the schools are like there? For a year, is it worth it?
What does your husband think you'd all get out of this year that would counter balance the potential stress/trauma, especially for your oldest child? Has he thought about what daily life would look like for you all, not just him? You say he's not keen on you staying at home - what does he think you'll be doing, job-wise?
If he's going to be regularly going back to the UK and leaving you on your own to look after the kids in wherever you end up in France, are you ok with that? It's quite a change from your current way of living, it sounds like - don't underestimate the impact this will have.
Honestly, personally, I think this is madness. And I have lived in France, liked living in France, and would do so again. But I wouldn't uproot my kids for a year, put them into a completely different school system, in a language they may not speak, give up my job that I like, find a place to live, sort out healthcare coverage, bank accounts, self employment registration (used to be a nightmare; might be simpler now, but I wouldn't hold your breath...), tax registration, try and find a new job, etc. Just because my husband was feeling a bit bored with how things are currently going in life.
I'm sorry not to be more positive, but there are lots of potential problems with his idea. He needs to think hard about the practical issues with this dream - and ideally, he needs to realise it's not you being difficult and trying to crush his dreams, or else there's a pretty high risk he'll resent you for not doing this insane thing and screwing up your family life.