It's really important to be clear with them that you both still love them and that will never change. I think the simple terms you have used above will lead them to worry that you may stop loving them if they make you sad or angry and lead them to be worried about upsetting you or being naughty etc.
Can you put it in terms of Mummy and Daddy make each other sad and we both want to be happy so we can be a good mummy and daddy for you.
So we have decided that we won't be so cross all the time if we live in different houses. Daddy is going to move to a new house (or you) and you'll be able to visit and stay with him and we will sort out the days so you know when this will be (or have decided this will be on xyz days, daddy will pick you up from nursery on xyz day etc).
Let them know it's ok to be sad about it ad that they can talk to you if they feel that way - If you feel sad or miss daddy/mummy you can always phone or skype to talk to daddy/mummy when you are at the other house (only promise this for dad if he agrees to it, otherwise only say it for yourself and maybe put some provisos in so they're not asking for it all the time or when they don't like being told off so ask for daddy instead kind of thing).
Tell them that the love a mummy and daddy have is different to the love a mum and dad has for their children. 'It doesn't matter how upset I am with you I will never stop loving you and I know daddy feels the same.'
Then it's big hugs all round and ask if they have any questions.
If you can do this together so much the better. But your ex sounds very biter and may not be prepared to do this yet/ever. You need to remind him that his current choice of words will have a significant impact in the dc's emotional wellbeing and that he needs to think carefully about their wellbeing and best interests rather than using them as pawns to try and get at you by saying things he may come to regret later. He will probably throw it back at you and blame you for him having to say this yadda yadda. But you know that's not true.
Try not to show that it gets to you because he is saying it to manipulate you knows that it will affect the dc and you will want to protect them from it. Or he may just be so angry that he doesn't care or can't comprehend the effect it will have on the dc. Tell him that calmly too if you think it will help. 'I understand that you are angry and if you weren't so angry you'd hopefully realise what a huge impact that would have on the dc so I am asking you think on it some more before you decide to go down that route'... Or some such if you can manage to be civil with him.
It may be worth suggesting councelling so he and you can get your anger out in a more controlled environment and then you can hopefully move beyond it and start thinking about the dc and not about hurting each other. Expect the first couple of sessions not to be very useful in working out contact etc, they are more likely to be used to get out all he wants to say and hopefully once he's got past that he will start to calm a little and think more of the dc and future plans for them.
If he does say things like that to the dc simply say to them that you don't know why daddy says that, that he is upset and angry still and we all say things we don't mean when we are upset, and then say how you see it instead (as above).
You can possibly use it as an example of how it makes you sad and how you get cross with each other (make sure it's with each other not you getting cross with him or him with you) if he keeps using it. Or simply say that daddy has a different point of view to you on this.
It's never easy, but kids are resilient and yours are young enough that they will accept it without lots of questionning hopefully. It can take a lot longer for your ex to calm down though and may be years before you and he can be civil enough with each other to put the dc ahead of the personal pain felt.