You can and should tell them without blaming. They may ask what happened. Why. And you can share with them, that stuff, too.
But age-appropriate.
In my opinion, It is absolutely appropriate to tell them you did not (do not?) want the marriage to end. I think it is utter bullspit to say "we've decided together to get divorced" when that is just not true. I'm certainly not going to lie to my kids that way. "we've decided...."
You'd better practice what you will say, to make sure you're not leaking anger when you tell them. Just the facts!
