There's no easy way through it. My youngest was 17 and I can still see his face when his dad told him.
I'd wait until it's a little closer and you're further from the holidays so they don't associate it with the holidays in their mind.
A month is too long for anticipation anyway. Maybe a couple weeks before.
Don't let your H do it alone - they inevitably try to paint it as a joint decision or as your fault. I know some sources say to present it as a mutual decision but I think that's a mistake - it's ok for the kids to know this is not your idea.
On the other hand - your kids need to know ITS GOING TO BE OK. You need to be strong for them, they need to know you'll be ok because you are their rock. Cry your tears elsewhere. Put on a valiant face and don't act like it's a huge deal because the bigger deal you make of it, the more scared they'll be.
Others with younger kids should have more specific advice.
