The Howards decide to visit one of their relatives who lives at the bottom of a hill. They decided to travel by putting roller skates under their sleigh and riding down the hill.
I don't see why this was rated so highly (4.25 before I got to it. Nostalgia? First published 1964).
Some . . . gophers? Guinea pigs? . . . rodents or lagomorphs, anyway, decide to go sledding (in spite of it being summer or late spring - whenever tiger lilies are in bloom, anyway). The kids fall off. The cake falls off. They all have a merry time anyway.
It's a bit Moomin-esque, but with very little of the charm. If you like this, may I recommend Tove Janssen?! ;)
The OpenLibrary scan cuts off the text a little (though it can still be read).