Hi kitkat,
For me, this would depend on a number of factors.
Does your ex have contact with the children or not? If he does, how would it impact on you if you had to drive a certain distance or length of time for handovers?
Are your children in primary or senior school? If senior school, how close are they to taking exams?
Do you have long standing friendships where you currently live? If so, would moving away impact on that and how often you would see friends?
Moving to be near a family member is good if they are going to be an active support network and a positive male role model to your children on a regular basis. Moving near to him just to be around him every so often, or for ’emergency’ situations, perhaps not so important?
New starts are positive things for some people and feared by others. You need to weigh up what is best for you and your children and go for that option.