West End Gardens Play Area, in Marine Road West, was damaged at some point between Saturday and Sunday, and the incident has resulted in the park being close.
A Lancaster City Council spokesman said the damage had cost around £900 to mend. The park is due to reopen this evening, Tuesday.
A police spokesman said: “We are appealing for any witnesses or anyone with any information which could assist us in this criminal damage enquiry.
“As you can see this is mindless damage. If you can help us then please call 101 or 01524 596986 and quote log LC-20160619-0646.”