How can I tell the difference between a boy and a girl kitten?

One way to tell the difference between a boy and a girl kitten is by looking at their genitalia. Male kittens have a small distance between the anus and the genital opening, while female kittens have a larger distance. Another way is to look at the shape of their genitalia - males have a rounder shape, while females have a more slit-like shape.