The problem you have is that if the proposed contact takes place when your son goes to school and there is any possibility of the schooling arrangements being disrupted, you could place the mother in the position whereby she can get into trouble with the LEA. If you are prepared to get your son ready for school and it is reasonable for you to do that, you may have an argument. Without the mother's agreement though, she could simply deny contact and by the time the court has accepted enforcement proceedings or varied the order, it will be too late anyway.