Barry Prendergast had been chosen from hundreds of candidates because of the home he and his wife, Naomi, had built for their 12 children in Colorado. He was, said the judges, an example for others to follow and he and his wife had "epitomised committed parenting".
Or perhaps not. Mr Prendergast, it has now emerged, is not quite the mild mannered teacher he had been portrayed to be.
What he had forgotten to mention when accepting the honour is that he was a leader of the Children of God, a cult started by the late David Berg, which has been repeatedly accused of child abuse and prostitution and whose female members work as "happy hookers for Jesus". Zach, as Mr Prendergast liked to be called, is remembered as leader of an indoctrination camp for children in Italy.
Confronted with these claims, 50-year-old Mr Prendergast returned the award. Gary Jarmin, spokesman for the National Parents Day Foundation, which organises the high-profile event, could only say: "There is nothing in the information we received on them to indicate that they were involved in anything like that."
At the Capitol Hill ceremony, Mr Prendergast had advised parents: "Anything that can enrich your relationship with each other as a family ... that's pretty much what we've been doing here." The Prendergasts offered a comprehensive service - while father and mother had organised parenting skills classes in the neighbourhood, the children had gone around as "Sound of Music- style family singers" to schools and nursing homes.
Yesterday, there was no answer at their home in Longmont, Colorado. But back in Merseyside, Mr Prendergast's mother, Betty, 69, would not hear a word said against her son. "Never in a million years would he be involved in anything like that. Maybe because he was in the Children of God made him give back the award rather than have any trouble.
"I think he is the victim of a slur. It was a shock hearing he had won the award in the first place and I was very proud, now I am just disappointed. He is the father of all those children and a very happily married man."
Mrs Prendergast said she knew little about the cult. "I remember some people being thrown out of the organisation. That was in the Seventies and Eighties, but I don't really know anything about it."