Whenever you are making the case for more or less contact, stress the ways in which this is what is best for your children rather than what is most convenient to you. You must show that their needs and wellbeing are your first concern.
If you are in dispute with the father about him having contact with your children, make notes on every contact visit, e.g. if he arrived on time, and how the children were when they returned – clean, fed, happy, distressed, crying, scared . . . Note how the children behaved before and after, and what they said about the visit.
Ask other witnesses to do a statement. If anyone sees the children before and/or after the contact with the father and notices how the child is, ask them to put it in writing. Any observation from a witness can be helpful.
If your children live with their father or other relative under a Child Arrangements Order and you want more contact and/or unsupervised contact, you can apply to the court to change the contact arrangements.
If a parent ignores or changes the Court Order, you can apply for an Enforcement Order  and there will be a court hearing where you say what has happened and that you want the Court Order to be enforced.
If you are worried that the father might take the children out of the country or away from your care, you can apply for a Prohibited Steps Order .