Railway Children by Edith Nesbit

The story concerns a family who move to a house

near the railway after the father is imprisoned 

as a result of being falsely accused of selling 

state secrets to the Russians. The three 

children, Roberta, Peter and Phyllis, find 

amusement in watching the trains on the nearby 

railway line and waving to the passengers. They 

become friendly with Perks, the station porter, 

and with the Old Gentleman who regularly takes 

the 9:15 down train. He is eventually able to 

help prove their father's innocence, and the 

family is reunited.