Young vandals have set fire to a playground 16 times in less than a month, Merseyside Fire and Rescue Service (MFRS) said.
Swings, slides and climbing frames have been damaged after a series of fires at South park, Bootle.
Firefighters said the arson attacks were "a huge drain on resources" and lives were being put at risk.
The fire service is urging parents to speak to their children about consequences.
MFRS is investigating the fires with Merseyside Police.
Michael Buratti, community safety coordinator at MFRS, said rubbish bins, shrubbery and playground equipment had been targeted.
The fires took away valuable assets from the local community, he said, adding: "What might seem like 'a laugh' now could lead to a criminal record."
Sefton community policing Ch Insp Mike O'Malley said fresh air and exercise was vital, particularly during the coronavirus pandemic.
"For local people to be frightened and fearful of visiting a green space will not be tolerated," he said.