Forty years ago, the Old Moor RSPB reserve in South Yorkshire’s Dearne Valley was part of the biggest rail marshalling yard in western Europe.

But what was once a harsh landscape of coal mines and heavy industry has been transformed into an 800-acre nature reserve with a lake, ponds, reed beds, woodland, hedgerow and meadow. The lake and ponds were formed when old mine workings collapsed. Over the years, rain filled in the resulting craters and nature took over.

Birds have always lodged here, but with the improved environment it has become the best site in the UK to see lapwings and tree sparrows. The arrival of a great white egret from the Balkans caused much excitement a few weeks ago.

The wind turbine next to the reserve’s car park is also a sign of greener times. Old Moor’s electricity is generated by solar and wind power and a woodchip-burning generator. The toilets are flushed by rain water. In the shop, a meter shows how much electricity has been generated from the renewable sources and the carbon emissions saved. I grew up in this valley at a time when there was always smoke in the sky and schemes such as this are heartening to see.

Old Moor opened last January and has quickly become a favourite with adults and children alike. When I visit with a Year 2 class from Brinsworth Manor Infants in Rotherham, Paul Higgins, the teacher and guide for the centre, is almost as excited as his young visitors. “Look at them”, he says. “It’s the intensity in their faces and the wonder when they find something. It doesn’t get much better than this.”

Paul is a genial, grizzly bear of a man who has been working at the reserve since it opened. And the thrill has yet to wear off. “It’s an exciting place to work,” he says. “I’d still come, even if they didn’t pay me.”

It’s a day of discovery and investigation for the group and before the pupils set off they are given a shoulder bag equipped with a magnifying glass, a small lens, an inspection pot and an information sheet. Soon they are busily searching for tiny creatures, picking up stones and logs and sweeping collecting nets through the grass.

Suddenly, two boys rooting through a mass of leaves find something.

Jonathan Ripley, seven, lifts up his hand and is astonished to see a sleepy tortoise shell butterfly on his finger. His friends gather round and he holds his finger out. The butterfly flutters and lands on Jonathan’s coat.

He stands still until it flies off.

Then a caterpillar is found by the deputy head Christine Dixon. This is not any old caterpillar but a big hairy tussock moth caterpillar.

After lunch we go to the hides. First the garden hide which has a ceiling covered with netting and felt leaves. Chaffinches, blackbirds and robins arrive. Collard doves and wood pigeons descend. Then it is over to the mere hide, for which everyone is given a small but professional-looking telescope. We can see the entire lake with its islands. Mallard and teal ducks and a lone coot are bobbing near the reeds, dozens of lapwings are dipping and weaving. It is a panoramic view with isolated hills in the distance. This is a magnificent book illustration come to life.

The children are loving every minute and like many before them, they will return at weekends with parents and grandparents in tow.

* Old Moor is open from February 1 to October 31. Admission pound;1.25 per child, adults free