The run is organised by the Friends of Churchfields Rec and will take place from 2pm to 4pm on Saturday, March 28.
The group is trying to raise a total £110,000 to improve the ageing park on Churchfields Road.
So far, the group has raised most of the money through grants and donations.
Support has come from Bromley Council’s Jubilee Fund, UK Power Networks, the National Lottery and local residents – but between £10,000 and £27,000 is still needed to finish the work.
In the current playground, a tire swing is broken, and part of the play frame is fenced off after a child was hurt last year.
Plans for the new space include a toddler play structure, a sensory zone, a climbing frame for older children, and a multi-gym for teenagers and adults.
Group member Amanda Spencer said: “The equipment is old and parts of it are unsafe. Older kids don’t have anywhere to play. But with the right support, we can change that.
“The council backs the project, but budgets are tight. It’s up to us as a community to make it happen. The children are leading the way.”
Many of the youngest supporters have been fundraising in their own ways. Some have sold second-hand books, baked brownies, and made balloon animals to help raise money.
Five-year-old Freya Cowling said: “I feel sad when I can’t play at the park because the equipment is old and broken. But I’m excited to do the fun run with my brother and raise lots of money.”
The group is inviting everyone in the community to take part or come along to support.
The Churchfields Rec Fun Run takes place Saturday March 29, 2pm to 4pm, at Churchfields Recreation Ground, Churchfields Road, BR3 4XP.
