Telegraph: Ben Davies had clambered onto the windowsill before tumbling out head first towards the concrete patio at his home.
The speed of his descent was slowed down, however, when he bounced off the line before he hit the ground.
He suffered a bang to the head as he hit the concrete and the first his parents knew was when they hear the noise outside.
They saw Ben looking dazed outside the three-bedroom semi detached house in Brinsworth, Rotherham, South Yorkshire.
His father Stephen, a print worker, was astonished to be told: "Daddy, I've just fallen out of the window" and paramedics were immediately called.
Ben, who has a brother Thomas, aged four, was taken to Rotherham District Hospital where he was examined and X-rayed.
He was kept in for observation for three days on a high dependency unit after having a fit, before being allowed home and given a clean bill of health.
Mrs Davies, 28, said: "The doctors say Ben is a walking miracle and had he not broken his fall by bouncing off the washing line it could have been fatal.
"It was sheer good luck he hit the washing line. The doctors said without it we could have been planning Ben's funeral."
Ben had been sent to his room for "time out" at teatime because he had misbehaved at school earlier in the day.
He climbed onto his bed and onto the windowsill before opening the window when he suddenly fell out.
Mrs Davies added: "I regard myself as a caring responsible parent but I have never locked the windows because of the fear of what would happen in a fire.
"But from now on I'll make sure the bedroom windows are locked and I urge all parents with small children to do the same.
"We are now having special locks fitted so that the windows open only three inches. Ben can be a mischievous lad and a bit of a handful and all this began because he had been sent to his bedroom for time out for misbehaving at school.
"In future if he misbehaves he will not be going to his bedroom. We now have a naughty chair in the dining room."
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