Agreements or MOU's that become final orders of the Court will have to be revised by filing a Petition to Modify the Custody Order. If the agreement was reached at mediation or is otherwise a temporary or interim order, then it can be modified at the final hearing before a Judge. If the agreement was entered in front of a Judge, and the Judge left something out by mistake, then a Motion for Reargument or Motion for Clarification can be filed within ten (10) days of the Court's Order. Some particulars about visitation can never be explicit, as flexibility and cooperation are often required when raising children. But, the problem with divorced or separated parents is that they often don't agree about much. Think about hiring a counselor or a parenting coordinator to mediate disputes and make life better for the kids.
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