Denmark's parents are reluctant to say whether they honoured the offer – but many may have found the proposal by kindergarten staff on the country's eastern island of Fyn hard to refuse.

Workers at the island's Grasshoppers nursery promised parents two hours of free childcare on Thursday evening – to enable them to stay at home and make more children.

"Quality copulation time" is an attempt to combat Denmark's low birth rate and growing population of elderly people. The country ranks 185th on the birth-performance list of the world's 221 countries.

Dorte Nyman, spokeswoman for the kindergarten, said the lack of young children on Fyn threatened the future of local nurseries on the island and had prompted them to search for a solution: "We have 42 children in the kindergarten and we'll be looking after 20 of them tonight," she told the BBC on Thursday.

She said the low birth rate and cuts in funding from local government had put nursery jobs on the line. "Without money we can't look after the children well, and if there aren't enough children, there are not enough jobs for us," she said.

Staff at the Grasshoppers nursery laid on a special party for the children with food and music on Thursday night. Any who asked why they were staying in the nursery rather than going home were told: "It's to give your parents a chance to speak at home."

However, many of the parents who allowed their children to attend the party were bashful and declined to say whether they planned to honour the nursery's offer in full. "Lots of them said: 'We'll bring our children to the party but you won't be getting any more kids out of us,'" Ms Nyman said.