This is the story of four children - very much wanting to be like the four children of E. Nesbit's novels - who discover a magic talisman that grants wishes. Halfway, that is. If you wish to be home, you'd end up halfway there. A wish for an animal to be able to talk produces almost-language - or a cat that can do nothing but talk or be silent, in alternating bursts. And don't even ask what happens if you wish that you "aren't there."
Of course, the children involved quickly figure out a solution - math can be your friend - but that doesn't mean that their wishes are wish or safe. And the amount of trouble they get in is barely justified by the happy ending. However, their troubles make for entertaining reading, and remind you to be careful what you wish for.