The six children of Mick and Mairead Philpott died in the blaze that gutted their home in the Derby suburb of Allenton in May 2012. The parents are now in prison.
The serious case review was prepared by the Derbyshire Safeguarding Children Board, the Derby Telegraph reported. Glenys Johnston, the author, said the children's deaths "could not have been predicted or prevented."
Johnston said caseworkers missed some opportunities "to get to know the family better." But she said the children appeared to be happy and getting good care, even though their father was living with two women.
Philpott decided after his girlfriend moved out that he wanted revenge.
"There is no evidence whatsoever that the intention to start the fire that killed the children was known to any agency and I am of the view that the intention could not have become known prior to the event," Johnston said.
The report made a number of recommendations for changes in procedure but said the "sad truth" is that the fire was not predictable.