Recently-installed play equipment in the playground at Ilkley's Riverside Memorial Gardens has been damaged after a fire in the toddler area on Monday evening.
The fire was set on Monday teatime (14th November) and caused serious damage to play equipment, in particular the pirate ship.
Thousands of pounds was raised by local people, organisations and businesses for the major revamp of the park's playground which reopened earlier this year.
Fire crews who attended say the incident is being treated by West Yorkshire Police as arson.
Friends of Ilkley Riverside Parks Chair, Ed Duguid, said: "Up to five youths were seen in the vicinity of the playground between 6.15 and 6.25pm on Monday. If you spotted anyone around this time in the area, please report it to police.
"We have an increasing number of anti-social behaviour events in the park area with bottles being smashed, graffiti, young trees being vandalised and the fencing at the wildflower area being pulled down. We believe there is a need to extend the town's CCTV into the park areas, as we have got to stop this kind of behaviour."
In a Facebook post, Ilkley Fire Station wrote: "This evening at approx 1830hrs we attended a fire at the children's play park at the riverside gardens which unfortunately has caused damage to the ship structure.
"The crew used a water backpack to deal with the incident which is being treated as arson and left with West Yorkshire Police who also attended. We have taped the area off as a safety measure until repair works are carried out."
District Councillor Kyle Green said: "Thank you to the fantastic fire crews who stopped this being a worse incident. Disgusting behaviour by those who started the fire. Please do report any information about those who committed this arson to the police."
If you have any information about Monday's fire, you're asked to contact Inspector John Barker on john.barker@westyorkshire.police.uk or to call the police's non-emergency number 101.