Under an oil company settlement reached in the US state of Pennsylvania, two children, aged seven and 10, were told that any talk of fracking is a no-no.

Under the 2011 settlement, unsealed last week, plaintiffs Chris and Stephanie Hallowich were explicitly told that an attendant lifetime gag order -- under which they were never to discuss the Marcellus shale basin or fracking -- also applied to their children.

The Marcellus formation is a vast basin of shale containing untapped natural gas resources in the eastern United States, close to key energy markets.

However, the fracking process needed to exploit it -- in which water and chemicals are blasted into the ground -- has led to complaints by environmentalists and some local residents.

The couple had claimed that a shale gas drilling operation near their home had damaged their health, causing burning eyes, sore throats, headaches and earaches, according to the Pittsburgh Post-Gazette, which convinced a judge to unseal documents related to the case.

In a court transcript, Stephanie Hallowich says the couple agreed to the $750,000 settlement "because we needed to get the children out of there for their health and safety."

"We know we're signing for silence forever, but how is this taking away our children's rights, being minors now?" she asks, referring to her then seven-year-old daughter and 10-year-old son.

The family's attorney, Peter Villari, appears equally baffled, saying that in his 30-year career he's never seen such an order apply to minors.

Chris Hallowich argues that the two children will be growing up in the heart of the major US fracking region, with other children whose parents work in the industry.

"We can inform them. We can tell them they cannot say this, they cannot say that, but if on the playground --."

James Swetz, the lawyer for Range Resources Corporation, one of the two defendants, insists it is part of the deal.

"I guess our position is that it does apply to the whole family. We would certainly enforce it," he said.

However, a Range Resources spokesman interviewed by the Post-Gazette said the company did not agree with its attorney's comments.

"We don't believe the settlement applies to children," the spokesman told the newspaper.

Villari told the Post-Gazette he was not aware the children had been released from the agreement.

"I'd appreciate it if they'd put that in writing," he said. "It would be very nice to do that."