The families were supported by about 100 construction workers who gathered outside the safety summit in Westminster.
Anne Elvein, whose teenage son Paul was electrocuted during refurbishment work at Euston Station in 1989, said: "I just wanted to get in and confront some of the actual employers so they had to stand face to face with the bereaved and see how they felt.
"I passed a book about what happened to my son to Lord Whitty [health and safety under-secretary of state] and he promised me that he would read it.
"I'm disappointed I didn't get to the stage because then I would have been able to confront all the employers and tell them exactly what I think of them." Maureen Brenan, who lost her teenage son Michael in a site accident 11 years ago, said: "The security guards tried to manhandle us out of the building but we were determined to get inside.
"We spoke to Lord Whitty and Michael Meacher before we were invited into the conference hall like we should have been in the first place." Addressing the demonstrators, George Brumwell, general secretary of construction union UCATT, said: "Within all my years in the construction industry I have never had an employer come to me wringing his hands in dismay. Today things have changed. We have got the government on our side." A DETR spokesman said that deputy prime minister John Prescott met 20 of the demonstrators after speaking at the summit.
He said: "Prescott explained that he had called for the summit in the first place. There was no animosity."