My ‘ex’ (the father of my children) lives in Israel and wants them to visit him there. I am afraid he might not return them to the UK, where they live with me,according to a residency order. Are there solutions to this?

Yes, there are several options that would allow your children to visit their father in Israel, and give protection , of varying degrees, against their possible non-return, at the end of visitation.

These range from a notarized written undertaking by their father, in Israel, to return them to the UK at the end of visitation, through a written agreement, signed by each of you, and even authorized in court in both countries, prior to the visit, defining the purpose and conditions of the visit, and clarifying your conditioned consent to the children's departure from the UK, their country of habitual residence, and the father's undertaking to return them.

Notwithstanding these options, non-return of the children to the UK at the end of the agreed period of visitation to Israel would amount to a passive act of child abduction under the Hague Convention, but the above steps would provide added protection and would be aimed to offset potential defences.