Here's video of a little girl trying to convince her dad to sell her little brother for 54 bucks.  She looks like she's five or six, and the brother is three or four.

First she says there's obviously something wrong with him, so they should sell him to a pet store for $1. Then she ups it to $54 so they can buy him back when he goes on sale, and use the profits to buy a toy owl.

Seems like a savvy kid to us.