I think it's the fact everyone says how unhinged, unpredictable and dangerous Putin is, that he'll literally do whatever he wishes to do regardless of consequences. He isn't afraid of anything. There's rumours he's got a terminal illness, and is planning on going out 'with a bang'. Again, it's only rumours at the moment, but surely he knows he's not going to be able to live normally again after this so wont be phased by any punishments etc, what if he decides to just take us all with him
For your own sake, and your children's, you need to notice how much of what's driving your anxiety is (as you say) rumour. More than that, it's misinformed. There are links on these threads to a wealth of articles directly and indirectly discussing Putin's motives, written by well-informed and very experienced commentators. They offer more than cold comfort, they carefully disentangle what is driving Putin's behaviour, and the impression I'm left with is that he doesn't intend to wage nuclear war on Europe or anywhere else. It would take a great deal of provocation to change his mind, however the media might make it look, and despite his own apparent taunting.
If I'm wrong, you'll barely have time to notice, and neither will your kids. But what you need to focus on is weighing up the likelihood that it will ever come to that, which is extremely slim. So get on with the life you're so afraid of losing, keep things as level as possible for your children, and if you can, do something to help the plight of displaced Ukrainian people. Even just quietly wishing them peace is better for your mental health than keeping replaying fearful scenarios of doom in your head. From what I can make out, the war Putin has started is highly unlikely to develop into nuclear conflict, but it probably won't be over for quite some time regardless, and your best hope is to learn to live with that and don't let him take up residence inside your head. That's part of the weaponry he is prepared to use, but it only works if you let it. I know, because I'm prone to destabilising anxiety myself, and I've had to rapidly work on it this last week to stop it dragging me down. You can too. Get on with your life, keep things normal for your kids - sending them to school will take some of the pressure off you.
www.theguardian.com/society/2022/mar/05/be-open-be-honest-and-listen-how-to-talk-to-children-about-ukraine