A security firm previously employed on the construction site where the body of Conley Thompson was found said it had reported "numerous occasions" of children trying to get in.
Peter Taylor, manager of Security Guards UK, said the company was no longer employed on the site at Bank End Road in Worsbrough near Barnsley although its signs remained.
He said: "We were employed on the site until July 16. During the time we did report on numerous occasions kids trying to get into the site and various trespassers.
"If a security guard was on site then he would have spotted it and would have prevented it from happening. We are very sorry for the family's loss."
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