Bags full of laughing gas canisters were seized from the Cocoon in the Park festival in Leeds last weekend.
The festival, which is held in Temple Newsam, took place on Saturday, July 13.
Police confiscated a large amount of nitrous oxide gas canisters - known colloquially as laughing gas - from the event.
Sharing a photograph of the bags on Facebook, the West Yorkshire Police Leeds East Team warned about the dangers of laughing gas and urged parents to ring the police if they find any canisters in their children's bedrooms.
The team said: "Just a couple of the bags full of NOS GAS (nitrous oxide) that we seized from Cocoon in the Park on the weekend.
"If you find any of the silver canisters in your kids' bedrooms them please ring us, it can be extremely dangerous.
"Youngsters think there is nothing wrong with taking Nos Gas also known as laughing gas.
"But it is very dangerous to inhale nitrous oxide directly from the canister, and doing it in an enclosed space is also very dangerous.
"If you take too much nitrous oxide you risk falling unconscious and/or suffocating from the lack of oxygen. People have died this way. Not laughing now
"If you know or have seen anyone selling this then please ring the 101 number, all calls are confidential."
What is laughing gas?
Laughing gas is the common name for Nitrous Oxide, also shorted to nos.
It is an inhaled drug.
The Frank service said: "Inhaling nitrous oxide directly from the canister is very dangerous because the gas is under such high pressure. It can cause a spasm of the throat muscle and stop a person breathing."
This is a psychoactive drug and is covered by the 2016 Psychoactive Substances Act, which means it’s illegal to give away or sell.