The incident happened at the Omniplex in the Quayside Shopping Centre on Tuesday afternoon.
Fire crews freed the nine-year-old boy using a hydraulic cutter, socket sets and screwdrivers, after he got his hand trapped.
The boy was assessed by paramedics at the scene but did not attend hospital.
Two fire engines from Northland and Crescent Link stations attended the incident, which was reported on the Northern Ireland Fire and Rescue's Facebook page.
A child has been cut free from his seat by fire crews at a cinema in Londonderry.