Children are amazingly resilient. It's much easier when they're younger.
I remember telling mine (when aged 4 and 3) a couple of years ago. The 3-y-o was too young to understand but the 4-y-o got it immediately. Because they are younger, there was no immediate reaction like you'd expect from an older child. The reaction did come, but later - some weeks/months later, in the form of unexpected tantrums and the odd emotional outburst. I'd been expecting a meltdown on the spot, but that just didn't happen. It was a relief, as we all had time to process it slowly and the big drama I'd been expecting on the day just never materialised.
Best piece of advice I can give is to really own the news and make it ok in your head. If you show you're ok with it, that it will be a good thing, and you are feeling calm (even if you're not feeling it inside!), the kids will follow your lead. They will look to you for their emotional guide. If you're ok, they're ok.
That's not to say they won't be upset (especially if they have to change schools, Doneit, which will be challenging) but basically you need to be their rock. If they know you have their back, they will feel it's ok.
A good thing can be to try to do an activity when you tell them (I chose to be sitting in a park - not a park we go to often - but somewhere out in the open and therefore not too stifling) when I told them, and then planned another separate activity (coffee shop outing) immediately after. The aim is to impart the important information in a non-dramatic way, but in a place where you can have a bit of privacy, and where the kids can be busy with something physical. If you sit them down on the sofa and tell them eyeball-to-eyeball that can be quite overwhelming for young kids.
Anyway, 2 years on we're all in a great place. House much calmer, kids in a firm routine, the 4-y-o (now 6) even remembers clearly events that took place "when daddy still lived here", but doesn't get upset about it. They've processed it and moved on, and so have I.
Good luck.