It’s a miracle only made possible by the new $50,000 implants that have just been activated in her ears.

Indianna and her nine-month-old sister Dakoda, both born profoundly deaf, had their cochlear implants mapped on Wednesday. It was the first time either child has heard any kind of sound.

Surrounded by a sea of friendly faces including grandma, both parents, their sister and two aunts, the whole family made the trip from Albury to Canberra for the operation and the final switch-on.

The family was asked to keep their faces devoid of emotion to help the girls understand it was a positive experience, but parents Mark Williams and Jodie Brunton struggled to keep their tears in check.

‘‘It was intense, but just so wonderful,’’ Ms Brunton said. ‘‘I can’t wait to communicate with them.’’

Indianna was thrilled to discover that clapping her hands made noise and even hitting together two plastic containers became a fantastic game with the addition of sound.Mr Williams 35, is looking forward to introducing them to music and books.

''I'm excited. I can't wait to hear them say 'mum and dad' and to enjoy nature and birds - for them to have a normal life,'' he said.

''We are so grateful to the doctors and everyone.''

The girls' implants were provided by the Sydney Cochlear Implant Centre in Canberra, a non-profit charitable organisation. Sydney Cochlear Implant Centre audiologist Anne-Marie Crowe said the reason for the girls' deafness was unknown as the most common genetic tests for hereditary deafness were negative.

''They don't hear the way we do - for them at the moment it's just noise,'' Ms Crowe said.

''We don't normally do simultaneous bilateral implants on siblings on the same day so … it was a big day for everyone. We had both our surgeons, so two teams involved, and surgery went for about five hours on each child.''

She said the clinic is one of the few that do intraoperative testing on the implants during the surgery to monitor the quality of the signal.

''It gives us more information to use at the time of switch-on.''

Speech pathologist Toni Isaacson said the experience of hearing for children who are profoundly deaf could sometimes be scary.

''They have no concept of sound so it can be overwhelming,'' Ms Isaacson said.

''So we try and make it positive.''

She said it would be easier for Dakoda to catch up on language skills as she was younger.

''But we tell parents that there will be no difference by the time both girls start school … but you can see that both girls are very bright so it could be sooner.''