When you go to mediation, you have to accept that you are going in with the mindset of not winning everything at all costs. If you genuinely want to come up with an agreement that will, first of all, be in the best interests of the children, and second of all, be good for both you and your ex-spouse, then mediation is something you should consider.
It is important though to have as much information as possible available and reviewed before going to mediation to save everyone time and money. It is also probably essential for you to sit down with a lawyer and talk about what the alternatives are to mediation and what happens if you do not reach a mediated agreement. You need to know what a court could do with the facts of your situation.
The mediator that you choose will usually be an experienced family law lawyer, and the cost of mediation is something that you generally split with your ex-spouse in an agreed upon way. The mediator will have some ground rules such as not interrupting each other, full and frank disclosure of information, and an open mind. Also, the most important part of mediation is that what happens in mediation stays in mediation. You cannot later raise it in Court and say that your ex-spouse was willing to accept something in mediation.