The challenge involves recording yourself eating a lemon wedge then sharing the video on social media - with the hashtags #loveforannabelle, #dipgawareness, #lemonfacechallenge.

Each post is about raising awareness for the incurable cancer she suffers - DIPG (diffuse intrinsic pontine glioma) - and giving some joy to Annabelle.

The campaign also hopes to raise funds for the The Isabella and Marcus Foundation to support research into a cure for DIPG.

Earlier this year, Annabelle's mother Kathie told The Canberra Times of treatment her little girl was receiving in Mexico that appeared to be stopping the growth of the tumour.

Kathie said on Friday it had now been deemed too risky for Annabelle to travel overseas, especially after she suffered a serious setback last month and was flown from Canberra to Westmead Children's Hospital in Sydney.

Annabelle had a build-up of fluid on her brain, which had a devastatingly swift impact on her health. As her parents called an ambulance to their home, the little girl was losing consciousness, could not chew or swallow properly or sit up unassisted.

Emergency surgeons in Westmead installed a shunt to drain the fluid.

When Annabelle was recovering, her mother asked her what she could do to put a smile on her face.

She said she wanted to get the Lemon Face Challenge going in Australia, after other children with DIPG had started it in America.

Kathie said Annabelle was excited to see The Wiggles accept the Lemon Face Challenge and she would be meeting them when they performed in Canberra in December.

The only treatment option now available to Annabelle is radiation. She had a full adult-sized-dose three weeks ago, which helped to stabilise her.

"We're gradually getting her back," Kathie said.

"We'll still do whatever we can as long as it does not affect her quality of life."

That quality of life includes being able to attend her preschool - Miles Franklin Preschool at Evatt - for a couple of hours this week.

Kathie said the family had received exceptional support from the preschool staff.

Their only hope now is for a research breakthrough that could cure the cancer. That's why donations to the Isabella and Marcus Foundation are so important. It is a registered Australian charity that provides seed funding for DIPG projects which would otherwise not be funded by government grants.

Kathie, a public servant, and her husband Adam, a carpenter, are also grateful for the support they have received from the Canberra community. Neither have been able to work while they care for their daughter and two other children.

"There is no support for us unless we quit our jobs and go on the dole, which is something neither of us want to do," she said.

"We can feel the community's love and support around us, please continue to keep our amazingly brave Annabelle in your thoughts."

Donations to the Potts family can be made here.