My response:
I have no idea why your attorney would tell you to "hang onto" your private agreement with your wife concerning child visitation, because the reality of that so-called "contract" is WORTHLESS !
When it comes to dividing personal property and real estate, a private agreement is just fine; however, when it comes to child visitation, that contract has no value whatsoever.
That's because a "private agreement" concerning child support and visitation effectively would nullify the court's jurisdiction if it could be valid. Only a judge can approve a custody, visitation and support agreement, and thereby, make it an order of the court.
The courts ALWAYS maintain, supervise and control a custody, visitation and support arrangement. Therefore, until a judge sees it, approves it and signs it, such a "private agreement" is worthless.
So, to answer your question, you can't sue your wife for not letting you see your children under your private agreement. If, after you receive a visitation court order, and she "interferes" with your visitation rights, THEN you can ask the court to enforce the orders against her - - to includes fines, jail time, and in severe cases, loss of custody.
Good luck, and get a valid court order.
IAAL