Um, not sure if I have any wise words on this. My parents divorced when I was ten - not sure how old I was when daddy 'left'. We drove him to his new flat, which was very tough, but made it real for us kids. Went straight round to our lovely childminder afterwards, who was a close family friend - she and her kids (she was divorced herself) reassured us that it wasn't the end of the world and we would still see our Daddy, etc. etc. etc.
My mother did complain about our father to us - the temptation must have been irresistable because he was very shitty, about money and contact. But I wish she hadn't, in a way. Would still have noticed his crapness, but not had it rammed down our throat.
Things that helped - my parents explaining that they weren't going to live together but they loved us very much and Daddy would always be our Daddy and we'd see him regularly (every weekend at first, I think, or every other).
Essentially I think lots of reassurance that your parents both still love you (even if it's a lie on one side), that you will still live in the same house and go to the same school (if you aren't, lots of reassurance about what will happen and that it will be fine), reassurance from other people/children/aunties who have been there and, ideally, your mother not slagging off your father despite overwhelming temptation.
However, as teenagers we did enjoy the fantastic bitching sessions with mother about Dad and his new wife every time we came back from a visit. It was a way to offload and laughing about it helped. I dunno, some counsellors would say it's a bad thing in the long run, but helped us cope.
I ended up having counselling about my relationship with my father once I'd grown up, which really helped - my sister, who didn't, still gets very hurt by his behaviour (he's still in our lives, on his own terms).
What really helped, but can't be guaranteed, is that my father later became a single parent to my little half sister and learnt an awful lot about being a Dad. Made him a damn sight better ? although a bit too late for us and he's still very far from perfect.