The Railway Children (version 3) - E. Nesbit

When their father mysteriously goes away, three children and their story-writing mother leave their comfortable life in London and move to a little house, Three Chimneys, in the country. Free to roam the countryside, Peter, Bobbie, and Phil make friends and enjoy adventures in and around the nearby railway station, and wave to the passing train each day, asking it to send their love to Father. There are no magical adventures in this Nesbit story, but as usual her child characters are so realistic that you feel they are your friends!