Conley Thompson died in 2015 after falling into a vertical pipe on the Church View site in Worsbrough, a mile away from his home.
He was able to sneak onto the dangerous building site - described as a “magnet for children” by a judge in Sheffield Crown Court yesterday - because three quarters of the fencing surrounding it was inadequate, despite bosses at Howard Civil Engineering knowing that there was a substantial risk of trespass.
Conley’s body was found by staff working on the site on the morning of July 27 2015 after he went missing the previous day.
It has never been discovered how Conley fell into the pipe as no staff were onsite, and no adult had seen the boy throughout the course of July 26.
Theories include that he slipped, or that he chose to get inside it without knowing how dangerous it was,
Following a police and Health and Safety Exective (HSE) investigation ruling out foul play, bosses at the firm pleaded guilty to two charges under health and safety law after inspectors found the fence of three sides of the site to be dilapidated and have gaps.
The failings were damned as "lamentable" in court on Thursday.
Judge Jeremy Richardson QC said: “The main reason why the tragedy eventuated was because of the wholly inadequate perimeter fencing surrounding the site. It allowed access from a number of locations.
“The site itself was an inevitable attraction to children because large diggers were on site, rubble and rocks for climbing were there, and it would have been regarded as a wonderful adventure playground by a child.
“It was, of course, nothing of the kind, it was a building site, and was capable of being a death-trap for anyone who had no right to be there.”
"The company was aware of the risk of trespass, but much more important, the company could and should have reasonably foreseen that such a site, in a residential area, would be a magnet for children who would see it as an adventure playground with all manner of exciting objects within to play upon and explore.
!Those objects on a building site are capable of being a death trap. That is why it is essential to have a boundary which is capable of keeping children out. The fencing onto the road was ideal. The rest of the site was lamentably bad."
The firm, which has an annual turnover of £25m, was ordered to pay a fine of £600,000 plus almost £43,000 in costs.
Judge Richardson described Conley as a child full of “adventure” but did express his concern that he was able to escape parental supervision and access the site.
He said: “The deceased had a habit of entering the Church View Site. It would seem he found it both tempting and easy to access – as indeed it was.
“The precise movements of the deceased during Sunday 26th July 2015 are not at all clear or confirmed.
“It is a noteworthy and very unhappy feature of the case that he was not seen by any adult during the course of the day.
“That feature is a source of concern to me. A seven year old boy of the disposition of Conley needed a high level of supervision.”