This is a two-part answer. First, child support and visitation have nothing to do with one another. Second, the CHILDREN have a right to have a relationship with their Father. That's why you can't prevent parenting time. If your kids really don't want to see him, then you need to help them build a better, more bonded relationship. You liked him well enough to have kids with him, so he must have some redeeming characteristics.
If you fail to foster a positive relationship between your children and your father, THEY are the ones who will get hurt, and THEY are the ones who will resent you later. It may sound like a cliche, but when they hit fourteen and rebel against you, don't be surprised if they all start screaming to go live with their Dad, because they have an unrealistic expectation of who he is. You don't like him, and at fourteen they won't entirely like you for a little while, so by transference, he'll seem ok. They'll assume that you were the problem all along.
The point is, you don't ever want your kids to have any basis for blaming you for their relationship, (or lack thereof), with their father.
This advice is based upon limited and hypothetical circumstances. For an answer that is specific to your situation, please consult an attorney. The answering of this question does not create an attorney/client relationship, and the poster should seek additional information from qualified legal counsel. Many attorneys, like ours, offer no-cost consultations.