The youngster was left with blood "gushing" from his head after being shot and kept passing in and out of consciousness, a court heard.
Emma Horseman, 24, stands accused of telling partner Jordan Walters to shoot the toddler after asking the boy's mum: "How do you cope with them crying all the time?"
A jury heard Horseman and Walters were in their flat when mum Amy Allen arrived with her two children, Riley, aged two, and Harry Studley, aged 18 months.
The court was told Horseman told Walters while Harry was crying: "Shoot Harry, just to frighten him, to shut him up, shoot it at Harry."
Andrew Macfarlane, prosecuting at Bristol Crown Court, told jurors Allen visited Horseman's flat to be put in touch with the organiser of a lending club.
He said: "The circumstances of this case are both simple and horrifying.
"Parents in a block of flats in Bristol meet up on one Friday afternoon with their children and, within an hour, a baby is fighting for his life on his way to hospital."
The court heard Walters got an air rifle out from the kitchen cupboard, started to clean it and replaced two gas cylinders with new ones.
As he did so, Miss Allen's youngsters seemed upset, the court heard.
Mr Macfarlane said: "While the boys were upset Amy heard Emma say 'oh Amy, how do you cope with them crying all the time?'
"Amy replied, 'It's easy, you just give them attention, sort of thing'.
"Seconds later while Harry was crying, Amy heard Horseman say 'shoot Harry, just to frighten him, to shut him up, shoot it at Harry'."
With that, the court heard Walters aimed the gun at Harry and fired it right into his head.
Mr Macfarlane said: "The bullet penetrated Harry's skull. He was operated on as a matter of extreme urgency and fortunately his life was saved.
Horseman was interviewed for 85 minutes and made no reply to all questions.
It is the prosecution's case that Horseman's participation was to tell her partner to shoot Harry.
The case continues.