Child custody and parental rights questions?

OK my children’s mother, who I have been with for 6 years, decided to leave me for another guy. We were never married and all the children have my last name on their birth certificates. We have a 4 month old, a 2 year old, a 3 year old, and a 4 year old. She told me that she is willing to come get her stuff and sign stuff over to me. She has agreed to sign something stating that I have full custody and she can see them for a visit at my house with a week’s notice and under my full supervision. She has agreed to go have this notarized. What can I include in this doent that will help me the most in any future court cases dealing with custody and/or child support? Thanks for any help