Up to half of looked-after children who are reunited with their families eventually have to go back into care, studies show.
Research from Britain and the US reveals wide variations in the success of returning youngsters to their natural families.
Previously it was thought that the amount of time spent away from home was the most significant influence on the success or failure of a reunion, with those who were away for six months or more least likely to go back.
However, researchers now believe that a number of factors can affect a child's reintegration at home. The report Reuniting looked-after children with their families, from the Joseph Rowntree Foundation, found children who suffered neglect were among those least likely to return home.
Those with behaviour problems had the best success rate when being reunited. Even those who had been sexually abused also had a good chance of success if the perpetrator had been removed from the home.
The role of parents was also crucial. Frequent visits and an active interest in their child's welfare were important in sustaining the bond with the family.
American studies show reunion was harder among lone-parent families and where there was poverty, parental drug use and chronic mental illness.
English research, meanwhile, revealed that the composition of families often changed while the child was in care, for example with the separation of parents and arrival of step-families.
"The particular ways in which families have been reconstituted during a child's absence may affect the likelihood of a harmonious return," the study said.
The overview, by researcher Nina Biehal, called for closer inspection of the impact of reunion on families.
"Although few studies have examined outcomes for children reunited with their families, the findings of those that have done so raise questions about the qualify of social work assessment, decision-making and follow-up in respect of children who return home."
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