Wallace plunged from the third floor of a building in Pollokshields at about 10.20am yesterday.
He was rushed to Royal Hospital for Sick Children in Yorkhill but Strathclyde Police said he died a short time after arriving.
A member of the public raised the alarm after the incident. Alan McCann, 44, who lives in a block of flats opposite, was the first to arrive at the scene.
He said: “I was walking nearby and I heard one of my neighbours, who saw it happen, screaming. I ran round to the front of the building and I saw the wee man lying there.
“I put him in the recovery position and phoned the ambulance straightaway. I waited with the boy for ten minutes.
“I was rubbing his hands and his ears but he was in a bad way. I put a blanket over him. The paramedics were talking to me on the phone and told me to check his breathing but I didn’t want to touch his wee body.
“It’s a tragic day. God bless him. He was only four years old.”
The area in front of the block was taped off and police guarded the entrances to the flats. Forensic officers examined the window from where the boy fell, as well the grass verge in front of the block.
During late afternoon, two plain-clothes officers left the building carrying two large paper bags of evidence.
One resident of an adjacent block said: “It’s terrible tragedy. When my son told me about it earlier today, I couldn’t believe it. The flats are split level, so it would have been the bedroom window he fell from. These flats are getting pulled down soon, so quite a few are empty and they’re moving people out quite quickly.
“The windows are the tilt-and-turn type. You just need to turn the clip at the bottom to be able to push them open.”
Another neighbour, who did not wish to be named, said: “He had no chance falling from the top floor. It’s terrible. A few years ago, another wee boy fell out of a window in the same block but around the back.
“He pulled through but he only fell from the second floor.”
Local politicians have expressed their shock. Deputy First Minister Nicola Sturgeon, MSP for Glasgow Southside, said: “I am desperately sad to hear about this tragic incident in my constituency, resulting in the death of a young child. My heart goes out to his family and my deepest condolences go to everyone who knew him.
“It is impossible to imagine or put into words what his loved ones will be feeling at such a sad time.”
Norman MacLeod, SNP councillor for the Pollokshields ward, said: “Clearly, the proper authorities will require to undertake a full investigation into all the circumstances surrounding this incident but, in the meantime, I extend my most profound and heartfelt sympathy and condolences to the family, friends and relatives.”
Strathclyde Police said they are investigating the incident which happened in St Andrew’s Drive. A report will be sent to the procurator fiscal.