Two years is a long time in the life of an eight-year-old, but Lionel Kennedy still remembers the afternoon during COVID lockdown when he and his four-year-old sister Ella read the inscription on a bicentennial memorial at Sydney's Earlwood Oval.

"We came to the park for a play … and then we spotted the plaque," he says.

The inscription on the brass plate from 1988 dedicates the monument to "original landowner" John Parkes, an early European settler who was the recipient of a 50-acre land grant in 1816.

"We said, that's not right," Lionel explained.

"The first people here were the Bedigal people."

After a conversation with their parents, the siblings collaborated on a handwritten letter to the Canterbury-Bankstown City Council asking for the sign to be changed.

"They'd been doing lots of learning in school about the land they were learning on," said their mother Julia Kennedy.

"I said they could write a letter to the council because if you want to get something changed, that's kind of the process."

The council passed the letter on to its First Peoples Advisory Committee, where it reached Wiradjuri elder Jennifer Newman.

"My heart wells up with pride and joy when young people use the names of the clans of country," she said.

"Ella and Lionel didn't just ask for the plaque to recognise Aboriginal people, [they] asked for it to recognise Bedigal people … and that's really significant."

She described the process as an important act of truth-telling.

The committee's co-chair, Dharug elder Aunty Lyn Martin, also volunteers with the Aboriginal Education Consultative Group, which helps schools deliver lessons about Indigenous history and culture.

"The fact that these children have learnt enough in school to be able to say that this is First Nations land … it was quite exciting for me," she said.

"It's a really amazing thing because you know, they enjoy the lessons … but you don't really know that you're getting through to them until something like this happens.

Ms Newman said the committee engaged in a series of long discussions about whether and how to rededicate the monument.

Ultimately, a decision was made to leave the original plaque where it was and install a new one on the adjoining side of the obelisk.

"To repeat an act of erasure or cancelling of someone else's story is not something we would like to do … John Parkes is part of the story," Ms Newman said.

"So we thought carefully about how to take the words of 1988 and turn them into a new chapter."

This month, the council unveiled a new plaque rededicating the memorial to honour the Bedigal as "enduring custodians", as well as John Parkes, "descendants of the colony" and "people more recently arrived from around the world".

Lionel and Ella are happy with the change.

"[The Bedigal] were the first here and it's important to know about their culture," Lionel said.

Their parents hope the process will leave a lasting impression on the young activists.

"To have them so positive, telling their friends and their school, is just awesome," said their father Joe Kennedy.

"It shows what education does. It's great."