I want to answer your question, but am a bit confused. Do your kids know what is actually going on, or do the just sense there is upset, and that you guys are struggling?
I think that changes how you handle things. In our case the kids did not know the specifics. They knew that Dad had been being a real jerk the past 6 months, but didn't know why, in addition they knew I was stressed to the max prior to Dday. My H's whole personality changed while he was having his A, and I was struggling the whole time to figure out what the hell was going on. I suspected, but never had proof, and he denied until I did. He also had a life altering event during the A he had a massive MI (out of town) and it was a bit of a kick in the jimmies to him to wake the hell up. Unfortunately the A went on for another 4 months until I had proof.
So the kids knew he was being a jerk. I kept telling them that Dad was under a lot of stress at work, and was having a hard time separating that from home. After Dday - things changed, he was a bit better, less tempermental with the kids, but I was a wreck, and often had to leave a room to go cry. My son knew something was wrong, my daughter thought it was because dad had been 'sick', she was still pretty young.
I told them, and Dad told them that we were having a rough time, that we love each other, and that sometimes Marriages require a lot of work, and can be difficult. We also made sure they knew our issues had NOTHING to do with them. NO MATTER WHAT WE BOTH LOVED THEM MORE THAN ANYTHING IN THE WORLD. That was the truth. It was enough.
My oldest did his best to not fight with his sister, and they both were amazingly good in school during all of it.
Now we are 5 years out, and I am not sure they ever even really think about that time. If they do, I guess it didn't leave too much of an impact on them, and I am fine with that. Hell now whenever we quibble, and we do that often, more of a joking harrassing, playing manner, the kids will both chime in saying "Yipee Two Christmas's".
They can joke about it, because it is so far from the reality they know.