In North American Indian pictographs, they use a triangle to represent a child's heart and a circle for an adult's heart. When a child does something wrong, the triangle makes a number of rotations according to how bad the behaviour is and the sharp corners of the triangle scrape the heart.
In an adult's heart, the sharp corners are worn off and become a circle, so the heart doesn't feel the pricks of conscience any more. The Little Stinker's design concept has been developed from this triangular shape of a child's heart which can feel the pangs of conscience.