Speaking only as a layperson, I would absolutely recommend retaining a lawyer, especially since you have children. The most trivial thing could come back to haunt you and then you really would need a lawyer. You might as well have one from the beginning instead of finding out later that certain things were not spelled out in the do-it-yourself agreement. Even good friends can turn into bitter enemies when it comes to disagreements about children, property (everyone has some), visitation, etc. Good luck whatever you decide to do.