In my situation I have 2 sons 11 and 7 years old. I get them every Thursday, Friday, Saturday, & Sun Morning til 8:00 am. Since my son are young they are easily swayed into thinking that this was just like other divorce where they spend time with mom and some with dad. X wife of course already introduced the OM to them and since the way to a you child's heart is to give them anything they have wanted... PS3, XBOX360, Nintendo Wii, and a trip to Disney which includes being picked up in a limo. To them OM is cool. I don't say anything bad about the other side. Inside me I just have the urge to tell them how this happened, but I bite my tounge because I know someday they will ask me that question.
At first you feel that you have to compete... my advise, DON'T. Also you might feel the urge to ask the kids what goes on in the other house, my advise don't. It is better for you not to hear what goes on over there... it hurts, but when the divorce becomes official... go ahead and grieve, cry, but realize that you have to pick yourself up in order for you to function for your children. Try to create a new environment, atmosphere, and tradition, this way the kids can look forward to something when they are with you (frday night movies, or ice cream night).
For those who have older kids that knows who did what to whom, consider yourself blessed. Just encourage them to maintain a relationship with their Mom/Dad. If they harbor ill feelings towards them, guide them to do the right thing but don't force them... that will take time too.
Hopefully this helps