Wakefield Council has been criticised in an independent inquiry for not intervening earlier in the case of Craig Faunch, 32, and Ian Wathey, 40, who were jailed for 11 years for sexually abusing children.
Some key social workers were so in "fear" of being seen as homophobic that they failed to speak out against the men, said inquiry chairman Brian Parrott.
Staff said they were bullied, bombarded and psychologically pressurised by the men, and at times preferred to avoid contact with the couple rather then deal with them.
"Faunch and Wathey were in effect in control of their own placements," said the report released yesterday.
"It is clear to us that with the benefit of hindsight there were many opportunities for Wakefield Council to have intervened in different ways to those in which they did"
"Indeed, in this case much of the knowledge was not just available with hindsight – it was available at the time," the report added.
Dozens of indecent photos were discovered in a drawer at the men's house on Sides Road, Pontefract, a year before they were investigated for child sex abuse.
Faunch and Wathey fostered a total of 18 children aged between eight and 14 between August 2003 and January 2005.
During this time Faunch filmed two eight-year-olds naked in the shower, and Wathey made one teen watch porn.
Together they performed a catalogue of abuse on two 14-year-old boys, one of whom suffered from Asperger's Syndrome – a form of autism – at their former home.
Key signs of the systematic abuse – including photos of the young boys urinating found in 2003 – were missed, or overlooked, and more children were put into their care.
In September 2004 "an escalating pattern of concerns" against the men were logged, most notably demands for money, and "strongly voiced criticisms" of children and staff. Yet at a review meeting the panel was not made aware of any concerns, their fostering registration was re-approved and the age range extended up to the age of 16.
It was not until their final placement ran away from the couple's home on January 31 2005 claiming to have been sexually abused, that they were banned from fostering and investigated.
In summary the report blames both an outdated Wakefield fostering system, and certain individuals.
It does not resolve whether Faunch and Wathey were already "predatory paedophiles", or whether the four children they abused were the first.
Wakefield Council welcomed the completion of the inquiry. Elaine McHale, Wakefield Council's corporate director of family services, said many of the report's recommendations were already being applied.