Until this summer, the three-year-old, who has a cochlear implant, had to sacrifice his hearing for a swim, which made for an extremely jittery mum.

"If he was about to do something silly I could never yell 'stop', so I was always hovering 10 centimetres away from him," Mrs Williams said yesterday.

"When he was in the ocean I was absolutely terrified. If he had water in his eyes and he can't hear, it's so disorientating for him, and dangerous."

But this summer, Felix has put to the test a new waterproof cover for his cochlear implant.

He can finally hear all his mum's safety tips - and even the sound of his big sister sneaking up on him with a water pistol.

"At first I thought it was a bit of a gimmick, a plastic zip-lock type bag that goes over it and makes it waterproof but it's completely changed our lives," Mrs Williams, from Windang, said yesterday.

"It's the first summer he's been able to swim and hear at the same time. We have a pool and we live by the beach so it's made a huge difference to all of us and we're over the moon."

The new Cochlear Nucleus Aqua Accessory seals in the processing unit, cable and coil of a cochlear implant. It can be used in salty ocean water, chlorinated pools and soapy baths.

Without it, cochlear recipients have to remove their external sound processor, leaving them hearing impaired or deaf.

Felix, who was born with recessive genetic condition Connexin 26 deafness, received cochlear implants at five months old.

"He's always been reasonably confident in the water, but has based all of his skills on copying his sister," Mrs Williams said.

"For the first time, we can actually speak with him while he is in the water and help to teach him.

"For us, we feel much safer having him able to hear us yell out warnings. Not that he necessarily listens, as he still thinks head-first down the slippery dip is a good idea."

Felix has finally hit the surf too, past the point of just paddling.

"He could hear us explaining things and didn't seem scared at all, even after a few dumpings. He had his first surf on a surfboard and loved the sensation through the water," Mrs Williams said.

"He is laughing and participating far more with the family in the water. The whole time in the water just seems so much more fun."