The Railway Children begins with the observation that they were not railway children to begin with. Roberta, Peter, and Phyllis come from a comfortable middle-class family which suddenly changes for reasons they do not understand when their father is taken away, and they have to move to a small house in the country. One of the first indications of their altered financial circumstances comes when they are packing to leave:
“Aren't you going to pack this, Mother?” Roberta asked, pointing to the beautiful cabinet inlaid with red turtleshell and brass.
“We can't take everything,” said Mother.
“But we seem to be taking all the ugly things,” said Roberta.
“We're taking the useful ones,” said Mother; “we've got to play at being Poor for a bit, my chickabiddy.”
From this point onwards the theme of coping with the hardship of reduced circumstances is illustrated regularly and often. There are many things the children took for granted in their old life which they cannot have any longer. On their first morning in the new house, Roberta reminds the others that there are no servants here, which is why they do not have water in their rooms to wash. They run down to use the pump in the yard. At tea time, mother has to reprove Phyllis for putting butter and jam on her bread, telling her that in their new circumstances it is: "Jam OR butter ... not jam AND butter."
Despite these privations, the general spirit of the book is optimistic and shows how family solidarity and a spirit of adventure allow the children not only to cope with hardship, but to find much to enjoy in their new circumstances.