E. Nesbit 
The Railway Children [EPUB ebook] 

They were not railway children to begin with. I don't suppose they had ever thought about railways except as a means of getting to Maskelyne and Cook's, the Pantomime, Zoological Gardens, and Madame Tussaud's. They were just ordinary suburban children, and they lived with their Father and Mother in an ordinary red-brick-fronted villa, with coloured glass in the front door, a tiled passage that was called a hall, a bath-room with hot and cold water, electric bells, French windows, and a good deal of white paint, and 'every modern convenience', as the house-agents say.
There were three of them. Roberta was the eldest. Of course, Mothers never have favourites, but if their Mother HAD had a favourite, it might have been Roberta. Next came Peter, who wished to be an Engineer when he grew up; and the youngest was Phyllis, who meant extremely well.
Mother did not spend all her time in paying dull calls to dull ladies, and sitting dully at home waiting for dull ladies to pay calls to her. She was almost always there, ready to play with the children, and read to them, and help them to do their home-lessons. Besides this she used to write stories for them while they were at school, and read them aloud after tea, and she always made up funny pieces of poetry for their birthdays and for other great occasions, such as the christening of the new kittens, or the refurnishing of the doll's house, or the time when they were getting over the mumps.
These three lucky children always had everything they needed: pretty clothes, good fires, a lovely nursery with heaps of toys, and a Mother Goose wall-paper. They had a kind and merry nursemaid, and a dog who was called James, and who was their very own. They also had a Father who was just perfect—never cross, never unjust, and always ready for a game—at least, if at any time he was NOT ready, he always had an excellent reason for it, and explained the reason to the children so interestingly and funnily that they felt sure he couldn't help himself.
You will think that they ought to have been very happy. And so they were, but they did not know HOW happy till the pretty life in the Red Villa was over and done with, and they had to live a very different life indeed.