Feature Film Concept or TV series (storylined family fantasy drama)

Two American children on vacation in the Scottish Highlands discover the wreckage of a wartime airplane that sends them back in time to the 1940s.  Facing danger and adventure, the children are the only ones who can help the pilot complete what was his final, fatal mission: to rendezvous with a U.S. submarine off the west coast of Scotland and deliver a secret document he stole in Berlin. German agents, determined to stop them, pursue the children in a deadly game of cat-and-mouse across the spectacular Highland countryside. Meanwhile, in the present day, the children's mother is researching her family tree, without realising that her children's adventures and her findings are inextricably linked.