It seems like it could be Children of Winter by Berlie Doherty. It's about 3 siblings who stay in a cottage in the peak district and then slip through time to the 1660s plague.
Children of Winter is a historical time-slip novel set in the Derbyshire village of Eyam. Three siblings have to survive alone in a barn during the Great Plague of 1666. They long to know what is happening down in their village. Must they stay away?
