In Sixth Grade I started reading Robert Heinlein novels, and I suspect this was either the first or second of his juvenile science fiction novels I read.
Twin teenagers Castor and Pollux are very much like Fred and George Weasley in the Harry Potter novels; really smart and mischievous. They are Loonies (not to be confused with the one dollar coin in Canada, but rather Moon natives. They buy a junker space ship and try to renovate it but run into problems of their own, ultimately drawing in their family and grandmother along the way.
The twins want adventure and riches. They decide to buy and renovate bicycles. This doesn’t go well by the time the family reaches Mars. Along with this disaster, they also pick up a local pet, a Flat Cat. If you want a visual representation, I always think of the Star Trek (original series) episode, “The Trouble with Tribbles.” The flat cats begin reproducing at a rate that make rabbits look like monks. The flat cats are both a temporary curse and ultimately a salvation to the Loonie twins.
The sense of pioneering, independence, and freedom from the traditional burdens of society are dominant throughout the book. In 2017 it would be a refreshing read.