The incident took place at The Green Patch in Valley Walk at some point between 5.30pm on Sunday (April 24) and 8am yesterday morning.
They smashed the window of a new cabin and stole cash tins with a small amount of money in.
Environmental projects officer Sue McKay said she didn’t understand why they had been targeted.
She said: “We run a lot of after-school clubs for kids who live on the Grange estate and I just do not get why people would do this.
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“This is a good place which helps others and it’s the second time we’ve been targeted in eight months.
“We no longer keep money on the premises but they stole our cash tins and tried to jemmy open the office door.”
Witnesses to the incident or anyone with information should contact police on 101 or Crimestoppers anonymously on 0800 555111.