One of the biggest challenges I've faced is the children "playing both sides" when it comes to things they want. My ex and I have had to be extremely diligent in keeping our lines of communication open with regard to who said what. Rather than immediately believing the kids, we talk to each other and sort things out first. This process became extremely difficult when he re-married and his wife became very controlling and did everything she could to cut off contact between us. The kids suffered, and needless to say that marriage ended rather quickly because of the conflict she created within their household. My ex and I were able to resume our previous communication style and the kids are better off for it.