A hospital radiographer let her 10-year-old son start an X-ray machine on a schoolgirl, a disciplinary hearing has heard.
Tamitha Grey, 39, stood behind the X-ray machine as her son was heard to ask: "Are we ready yet, mum?".
The 15-year-old patient's shocked family heard her reply: "No...OK" before the radioactive machine whirred into life.
The schoolgirl's mother Nicola Jones said: "It was an incredible thing to see. I still can't believe it happened.
"It was an extremely emotional moment. After I got home I just could not stop thinking about it. It was ingrained in my mind."
Mrs Jones works as an ultrasound technician at the same hospital - Withybush Hospital in Haverfordwest, Pembrokeshire - where her daughter was X-rayed for a suspected broken wrist.
She said: "At the time I would have felt uncomfortable that he was there, but my priorities were my own daughter."
The boy was then taken away, before Mrs Grey performed a second X-ray on the girl.
Mrs Jones said: "As far as X-raying people in the hospital goes, it's a very private environment, and it was a surprise to see him there just totally out of context."
She said she did not realise the gravity of the situation until after the procedure was over.
The hearing was told Mrs Grey took her son into hospital after his after-school rugby match had been called off.
She has already been given a formal written warning after an internal investigation where she admitted letting her son press the button to start the X-ray machine.
Now she could be struck off for misconduct in the hearing of the Health Care Professions Council.
She accepted the HCPC's allegation she permitted an unqualified and unauthorised person to initiate the exposure of a patient to ionising radiation on May 9 last year.
She also admitted permitting a member of the public to be present during a clinical examination, and that both allegations constituted misconduct.
But she denied that her fitness to practise as a radiographer was impaired by her actions.
Sophie Lister, on behalf of the HCPC, said Grey's son had been in the X-ray department of the hospital from about 4pm after an after-school rugby match had been cancelled.
The hearing was told children were allowed to stay in the staff room while parents worked if they had problems with childcare.
Miss Lister said: "By allowing her child into a clinical area and letting him press the button she breached guidelines that indicated only fully-trained practitioners were authorised to carry out X-ray exams."
Mrs Grey - who worked at the hospital for 10 years - appeared before a fitness to practise hearing of the Health and Care Professions in Cardiff, accused of misconduct.
She was given a final written warning by Hywel Dda Health Board after an earlier internal investigation.
She then referred herself to the HCPC, who are set to decide whether further punishment is needed during the three-day hearing.
The panel heard from other witnesses who said the mood at the time was relaxed - and that consent was assumed unless parents objected when accompanying minors into exams.
They were also told Mrs Grey's son had been brought to the clinical area by a line manager.
The hearing in Cardiff is continuing.