My dcs were the same age. I told them that we were going to have two homes, one for mummy and one for daddy and that we needed to be friends now instead of husband and wife. Just make it sound normal and answer any questions. They'll just want to feel safe in the knowledge that you, their parents know what you're all doing, and crucially, what things will be like for them. So, you'll stay at dad's on some nights, you'll still go to school, swimming, whatever.
They don't need an emotional outpouring from the adults.
Having been sat down with my younger siblings as a child of 10, and told by both our parents together, almost formally and sounding very scripted, a kind of emotionally charged announcement, with hidden agendas and shifty expressions, I preferred something different when it came to my own dcs. I realise my parents did what they thought was best, and I know some people believe it's best to tell the dcs together, but I strongly disagree.
A calm conversation, fairly matter of fact, that we don't work well living in the same house as each other, so we're going to change the way we do things, but all will be well.
