Yes! WhatsApp communications or any other written or oral exchange with your ex-wife, that express your objection to your son’s move to another country, will serve as evidence. For example, the District Court in Lod (2^nd instance) rejected a mother’s appeal on the family Court’s decision to return the child to New York, USA. Similarly to the Family Court, before, the District Court took into account the father’s written messages who expressed his objection to his child’s travel to Israel to the mother and ruled that these support the father’s claim and therefore the child (a daughter) should be returned (Case # 2298-10-24).