It's merely a chance for the two of you to try and find a way to work out some differences of opinion and come to some sort of agreement regarding your child(ren).
In my experience, you can take any document to mediation that you wish. However, when I offered documentation to our mediators, they had NO interest in reviewing them.
Mediation is a great concept, if it's offered to two parties who are willing to be flexible and willing to keep an open mind. This is usually not the case when it comes to divorce/custody/visitation/child support issues.
My best advice is; focus on what's best for the child(ren)- not what's best for you or the other parent. Good luck to you, and to your child(ren).
"Whoever established the high-road, and how high it should be, should be fired." Sandra Bullock