Reggie Mears, 8, was playing outside his home in Wecock Farm, Portsmouth, when the freak accident happened last week.
A brick, possibly dropped by another child, struck him on the head while he was riding his scooter below the balcony, fracturing his skull and exposing part of his brain.
Medics rushed little Reggie first to Queen Alexandra Hospital in Cosham, before he was decided he would undergo emergency surgery at University Hospital Southampton to fit a metal plate in his skull.
The Denmead Junior School pupil has since been released from hospital to recover from his home in Fulmer Walk.
But now his mum, Ocean Parrack, has spoken of her family’s petrifying ordeal and admitted they now face an anxious wait to see what lasting damage has been caused by Reggie’s head injury.
She said: ‘The wound was so deep it exposed his brain. Now we’re looking at such a high rate of infection. If he gets an infection in the brain it could be lights out for him. We’re still on edge. We're really petrified.’
The horrifying incident took place on Wednesday of last week shortly after 12.30 when Reggie was playing.
The brick dropped off the balcony just as Reggie rode under it on his scooter.
Neighbours nearby rallied to his aid, with one woman – a trained first aider – providing treatment to the tearful lad.
Recounting the moment she saw her baby boy caked in blood and screaming Ocean said: ‘There was so much blood on the floor. I’ve never seen so much of it in my life... Reggie was distraught by it all.
‘It was so lucky a woman who was a first aider was there helping. She was amazing. I wouldn’t have had a clue what to do.’
Reggie now faces two weeks off school while he recovers and has been told to stop playing football indefinitely.
As well as having to have a plate fitted in his skull and stitches to repair the wound, Reggie now suffers from horrendous headaches and is on antibiotics to stop any potential fatal infection in the brain.
Ocean added she was furious that a child might have dropped the brick that hit her son and has now demanded parents keep a closer eye on their children when they play.
She said: 'It’s been called a freak accident. But if Reggie was any younger, we would have been looking at arranging a funeral. Doctors said his skull would have been too soft to take the impact. That’s what was scary.’
Hampshire Constabulary said the force was investigating the incident but said no arrests had been made so far.