Imo, and ime, children don’t need to know the ins and outs of it.
exH and I picked a day (well, I eventually made him pick a day, as he was dragging it on and on), and just told each of the dc. We did it separately, as that suited our dc better, but all in one go, so all done in the same morning. We said something by along the lines of “we have decided we don’t want to live together anymore, and are getting divorced. You will all continue living with mum, and will have lots of opportunities to see dad. He will be moving out on X date (was about 6 weeks away), to Y house (is 5 minutes away). You will spend some of the school holidays with him, and we will share weekends like we have been doing here recently (which meant EOW). We both love you lots, and this isn’t anything to do with you, it is problems between mum and dad. You will have lots to think about, and lots of questions, so we can talk about those when you are ready” and then gave them some space to think about it. They had questions, obviously, but we didn’t want to put them on the spot. Dc were (then) 13, 11 and 7.
dc1 was confused (SN), but fine with the explanation, and happy to stay with me. Had to do lots of reinforcing of the main messages I’ve the next couple of weeks as she processed it. Dc2 wasn’t surprised in the slightest, and only concern was that she was able to stay with me as didn’t want to live with exH at all. Dc3 was quite upset initially, but also mainly concerned about daily routines etc, and I was able to reassure him that it would still be me doing all the school stuff, and that he would see his dad lots, and be able to speak to him every day if he wanted to (this dropped off fast for him, only dc1 speaks to exH daily now)