Here is a paragraph directly from the Watchtower library:
What, though, if one of the parents is disfellowshipped? Should the Christian parent make the child available for visitation? The disfellowshipping process of the congregation only alters the spiritual relationship between the individual and the Christian congregation. In fact, it severs the spiritual bonds. But the parent-child relationship remains intact. The custodial parent must respect the disfellowshipped parent's visitation rights. However, if the noncustodial parent poses an imminent and substantial threat to the child's physical or emotional welfare, then the court (not the custodial parent) may arrange to have visitation with the child supervised by a third party.
Hope that helps.