Currently I am negotiating a relocation agreement with my 'ex' whereby she can relocate with our children to Israel as long as I can see them afterwards, back here in USA and in Israel. How can I be ensure this?

There are several options, but it is recommended to make obtaining a "Mirror Order" of the U.S. settlement /court-authorized judgment in Israel, before the children leave American soil, a condition for relocation, plus up-front financial guarantees, depending on the circumstances. Our law practice advises foreign counsel representing parents overseas in negotiations for agreements which include relocation of children to Israel.