E Nesbit 
The Railway Children [EPUB ebook] 

When Roberta, Peter and Phyllis’s father is taken away and they move to a tiny cottage in the countryside, the only advantage is the nearby railway. Join them on their adventures as they befriend all those who work with the trains, prevent a railway disaster and try to discover the truth behind their father’s disappearance.
The Railway Children, a much-loved children’s classic, was first published in 1906 and has never been out of print.