Officers from Derbyshire Police responded to reports of a large group of youngsters at the Etwall Leisure Centre on Monday at around 1.05pm.
The Etwall, Hatton and Hilton Safer Neighbourhood Policing Team (SNT) said they were “horrified” to find the group had forcibly made their way onto the locked pitches.
The force said the youths made a “hasty” getaway after spotting police.
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The incident prompted police to issue a warning to parents, saying: “Do you know where your kids are? Do you know what they are getting up to?”
Police said they know the names of some of the youngsters involved and they will be “dealt with accordingly”.
In a Facebook statement issued after the incident, the SNT said: “It is of the upmost importance that you ensure your children are following the rules and regulations for Covid-19.
“If a child breaches the rules then as their guardian, YOU will be held responsible for paying the fine.
“This may seem harsh but we need to ensure these rules are being followed so that one day in the not too distant future, we can be lift the restrictions and start getting back to a state of normality.”
The statement continued: “A gathering of 20 is simply not acceptable and quite frankly irresponsible in the times we are all living through.
“Officers were also disgusted by the onslaught of rubbish that was just discarded about the place.”
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