The Railway Children (Edith Nesbit)

The classic adventures of three children who find their new home is near a railway line. When Father goes away unexpectedly, Roberta, Peter, Phyllis, and their mother have to leave their happy life in London to go and live in a small cottage in the country. The children seek solace in the nearby railway station and make friends with Perks the Porter and the Station Master himself. But the mystery remains- where is Father, and will he ever return?