Kenneth and the Carp by Edith Nesbit — Read

Kenneth's cousins had often stayed with him, but he had never till now stayed with them. And you know how different everything is when you are in your own house. You are certain exactly what games the grown-ups dislike and what games they will not notice; also what sort of mischief is looked over and what sort is not. And, being accustomed to your own sort of grown-ups, you can always be pretty sure when you are likely to catch it. Whereas strange houses are, in this matter of catching it, full of the most unpleasing surprises.

You know all this. But Kenneth did not. And still less did he know what were the sort of things which, in his cousins' house, led to disapproval, punishment, scoldings; in short, to catching it. So that that business of cousin Ethel's jewel-case, which is where this story ought to begin, was really not Kenneth's fault at all. Though for a time. But I am getting on too fast.