Some helpful suggestions for what to consider when talking to children about separation.  

In particular I agree that for this difficult conversation it is worth planning ahead.  

I would add that I think it helps for the parents themselves to have beforehand thought about what is going to happen going forwards and be aware of the options available. This is one of the first conversations I have with most clients as it means they can have a clear picture in their mind to avoid any unnecessary confusion or distress for everyone.