Horsley's Piper Williams was born without an iris in both eyes - a condition known as aniridia.

She has no vision in her right eye, and limited sight in her left.

The six-year-old also has some issues with mobility, after undergoing multiple reconstructive surgeries to fix deformities to her feet.

On top of that Piper has global developmental delay, an inoperable brain tumour and suffers regular seizures which can last up to 40 minutes.

It's tough on the little girl, who started Kindy this year, and it's hard for her family too.

But mother Stacey Retallick said their spirits had been lifted by the Bikers 4 Heroes group, which is hosting a fundraiser next month to help them out.

"We've always done everything on our own and the fact they're helping us is just overwhelming," she said.

"Piper gets some funding through the NDIS because of her limited vision, but because we don't have a diagnosis for what's causing her epilepsy and other issues she doesn't qualify for any other funding.

"With the medications, hospitalisations, specialists' appointments and tests, it can get quite expensive. So the financial support is fantastic - and the fact that someone just wants to help us has just blown us away."

Bikers for Heroes was set up to raise funds for the i98FM Illawarra Convoy, and its members wear superhero costumes. But Stu Butler (aka Captain America) said they're not the real heroes.

"Our name came about due to the fact that we're doing this for the real heroes, the children and their families doing it tough," he said.

"It's not fair that any child should become unwell and as parents we all thought that if there was illness in a family, quite often there is financial implications and more often than not the fun side of life takes a back seat.

"We want Piper's family to not have to worry financially and we want to be a part of restoring smiles and having fun. Piper is such a beautiful little girl and we are honoured to be helping such an amazing, strong family."

The fundraiser will be held at Flip Out Albion Park Rail on May 19 from 12-4pm.

"To watch Piper you might not immediately notice that she has very limited sight; that she can't run, jump, skip and hop like other kids," Ms Retallick said.

"You may not notice that she doesn't speak properly, that she takes some time to retain new information.

"You won't know that she suffers seizures on a weekly basis - sometimes for up to 40 minutes.

"What you will see is a happy little girl - and we'll do all we can to keep her that way."