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."
A construction site where the body of missing seven-year-old Conley Thompson was found by builders this morning was checked by police officers last night, the force have said.
Detective Chief Inspector Dave Stopford said the site in the Worsbrough area of Barnsley was checked "during the hours of darkness" by officers after Conley was reported missing just after 10pm last night and found to be securely locked with a large perimeter fence.
He said the investigation was declared as a "critical incident" and around 50 officers were drafted in with searches taking place throughout the night.
The youngster's body was found by construction workers at 8.30am this morning.
Det Chief Inspector Stopford added: “The investigation continues into the cause of Conley's death and we are working with the Health and Safety Executive as part of that investigation.”
Seven-year-old Conley Thompson died after he slipped into a plastic pipe on a construction site, his grandmother has said.
Deborah Fraser said: "He got in through a little hole at the top of the construction site. Because it was raining he slid down and went into a vertical pipe."
Paying tribute to her grandson she said he had "a smile that would light up a room."
The grandmother of a seven-year-old boy said she had warned him to stay away from the construction site where his body was found.
Deborah Fraser said he had played at the site in Worsbrough, near Barnsley, South Yorkshire before and she had warned him to stay away.
Gran of Conley Thompson confirms he died in tragic accident on construction site - he'd played there before & she'd warned him to stay out.
Developers have said they are working with police to investigate the death of a seven-year-old boy whose body was found on a construction site.
The body of Conley Thompson was found on the site in Worsbrough, South Yorkshire, after he we missing after going to play with friends on Sunday.
Developers Howard Civil Engineering said they were working with police to investigate the "tragic incident".
The site is owned by Erris Homes Ltd.
Police have said they are treating the death as unexplained and post mortem tests are due to be carried out to establish the cause of death.
We are co-operating fully with the police investigation into this tragic incident. While this continues, we are unable to comment further.
The babysitter of missing Barnsley schoolboy Conley Thompson has paid tribute to the seven-year-old after what is believed to be the child's body was discovered on a construction site this morning.
The locals I have been speaking with in the last hour have told me this construction site has not had much activity in recent months and it became something of a magnet for young teenagers predominantly to hang around, not so much young children.
But there is a gap at the back of the construction site that would be small enough for a child to come in and if that is where Conley was able to access there will be questions raised because there is a sign here that says there is 24 hour security watch over this construction site - clearly not the case because some child did manage to get in here last night.
Floral tributes have begun being laid close to the construction site where a child's body, believed to be missing seven-year-old Conley Thompson, has been found.
Police move the cordon back on Bank End Road after it is confirmed that a body has been found in the search for missing 7-year-old Conley Thompson
South Yorkshire Police have said they believe the body of a child found at a construction site in Barnsley is that of missing Conley Thompson.
The seven-year-old was last seen at a park in the town yesterday evening where he had gone to play with his friends.
Officers searching throughout the night for the missing schoolboy confirmed that a body was found around 8.30am this morning at Bank End Road in Worsbrough.
Conley's family have been informed and they are being supported by specialist officers.
We deployed our full resources with officers searching throughout the night to find Conley and we are deeply saddened by this tragic development.
While it is early in the investigation, the death is being treated as unexplained and a post-mortem will take place in due course.
Our thoughts remain with Conley’s family and friends at this very difficult time.