I have visitation rights in Israel. My ex-wife, who has custody, has flown to the States with our children behind my back. Can I bring legal action for their return if she is the custodial parent and I only have access?

Certainly, as under Israeli law you remain joint legal guardian with the mother, even though you are divorced, and she has custody. The Hague Convention will apply. Where visitation rights are infringed because of child abduction, the Convention is very effective in securing the children's return.