http://www.medscape.com/viewarticle/405852_7
Remarriage
One half of divorced persons remarry within 5 years.[7] Whether one calls them stepfamilies, blended families, or reconstituted families, remarriage is not a recreation of the two-parent family; it is another major life transition for the family. There are ex-spouses, grandparents, kids that did not grow up together who are now expected to behave as brothers and sisters, rearranged birth orders, and perhaps babies of the new union. There are children with multiple parents under the same roof trying to form a single unit. Visitation with the noncustodial parent means that children will be coming and going, making it tough to keep track of who will be where for dinner on the weekends.
There are the inevitable problems, such as how to refer to grandparents, cousins, aunts, and uncles from the family of the ex-spouse and the family of the new spouse. The boundaries of what we traditionally consider family blur, if not dissolve completely. No one has developed a template for adapting to all these sudden changes.
A collection of studies analyzed in Furstenberg's Remarriage and Step-parenting showed that stepfathers are well accepted by younger children when the mother is the custodial parent, but stepfathers might have problems with older children. Boys' difficulties frequently decrease when a male adult is added to the household, but girls react poorly.[7] Stepmothers in the noncustodial father's household integrate easily by becoming a friend to the children, but when a custodial father remarries, the problems for the stepmother can be considerable.[13] The children, especially older children, might not accept her or recognize her authority. They resent her, and if she dares to bear children with their father, they resent the babies, too. This phenomenon is not new. Centuries-old fables describe the evil stepmother and the resentment shown to her in the father's household.
