Objective To determine which aspects of divorced parents' ongoing relationships with their former spouses were associated with children's and youth's postdivorce well‐being. Background Research on the associations between former spousal relationships and children's postdivorce well‐being has focused extensively on postdivorce coparenting, with less emphasis on other aspects of these multidimensional relationships. Method Divorced parents (N = 641), recruited via Amazon MTurk, reported on six aspects of their relationships with their former spouses (coparenting cooperation, general communication with former spouses, boundary ambiguity, how often they talk with their former spouses, and satisfaction with custody and child support), and three indices of postdivorce child well‐being (prosocial, internalizing, and externalizing behavior). Results Analyses were conducted separately for children (4‐ to 9‐years‐old) and youth (10‐ to 18‐years‐old). For children, coparenting cooperation was associated with more prosocial but less internalizing behavior; general communication and boundary ambiguity—family system were associated with greater externalizing and internalizing behavior. For youth, boundary ambiguity—family system was associated with more externalizing and internalizing behavior, boundary ambiguity—relationship with former spouse was associated with more externalizing behavior, child support satisfaction was associated with more prosocial behavior, and custody satisfaction was associated with less internalizing behavior. Conclusion For child and youth postdivorce well‐being, some aspects of former spousal relationships appear more impactful than others, with boundary ambiguity appearing particularly detrimental. Implications Divorce education programs may need to diversify their content, supplementing the common focus on postdivorce coparenting with resources that help parents reduce boundary ambiguity in the family system.