because their ex cut them out

That is being too generous in your assumption. Family courts go above and beyond to try to maintain relationships between parents and children. If this guy wasn't a part of his children's lives it's either because he chose not to be or because he was so abusive that a judge decided that it was in the child's best interest to keep him away. Short of kidnapping one spouse can't unilaterally cut the other out of the children's lives after a divorce.