Why does leafpool give her kits to her sister squarlflight?

Because the warrior code states that a Medicine Cat is NOT aloud to have a mate or kits. Unfortunately, Leafpool falls in love with the warrior Crowfeather from Windclan and has three kits: Jayfeather, Lionblaze, and Hollyleaf. Since she wasn't aloud to have kits, she gave them to her trusted sister, Squirrelflight. For more info read Warriors: The Power of Three series.