The day I swapped my dad for two goldfish

the long version

This children's book is about a boy who chooses to trade his father for his friend's two goldfish. When his mother returns, she sends the boy and his younger sister on an adventure to return the goldfish and recover their father. However, when the boy arrives at the goldfish owner's home, he finds that his father has been swapped again. This continues, and as the boy and his sister venture throughout their neighborhood, they discover many friends have been a part of the "swap". Ultimately the boy returns his father, and is sworn to never swap his father again. He promises, but then eyes his sister as possible future collateral.