Hi Relate do a book on help for children, can buy it from them direct or i think amazon sell it too. I bought it for my 2 younger sons, then aged 12 and 17, but they both refused to read it. Also tried to get them to counselling, as it happened 3 years after their elder brothers death, but neither of them was willing, was a very long waiting list too.
Only other bit of advice i can give, 18 months after the end of my marriage, is be honest as you can, depending on their ages. Or as honest as you can without criticising their other parent, however much its deserved. I've somehow managed not to criticise my ex, despite his many threats, missing mortgage payments etc, i say we're short of money all the time, but not whose fault it is.
My only reward is i've still got the fantastic relationship i've always had with them, my ex due to his lies, other woman and refusal to see his sons lots of the time hasn't any more. So i guess my way has worked up to now.
Don't think it matters how old children are, it still affects them terribly, one parent going to live elsewhere, wish my ex would put our sons first, but he only seems bothered in himself and his happiness, so his way seems to be the wrong way to carry on.
Sending hugs to your friend, wouldn't wish this on anyones children.