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.
Leafpool gives her kits, Jayfeather, Hollyleaf, and Lionblaze, to her sister Squirrelflight because she believes it is for the greater good of the clan. Leafpool is a medicine cat and cannot have kits, so she chooses to keep this secret and allow her kits to be raised by someone else within the clan to avoid breaking the warrior code. Squirrelflight agrees to take on the role of their mother to protect Leafpool's secret and the well-being of the kits.
Leafpool hides her secret by confiding in Squirrelflight, who agrees to raise the kits as her own. Leafpool distances herself from her kits, Jayfeather, Lionblaze, and Hollyleaf, and the clan is led to believe they are Squirrelflight's. Only a select few, including Cinderpelt, her sister, know the truth.
Squirrelflight did not have any kits of her own. She raised Leafpool's kits, Jayfeather, Lionblaze, and Hollyleaf, as her own to protect her sister's secret that she had broken the warrior code by having a litter of kits.
Leafpool and Crowfeather had kits between the second and third series.
No, Leafpool is not the mother of Squirrelflight's kits. Squirrelflight's kits, Alderheart and Sparkpelt, were actually born to Squirrelflight and Bramblestar. Leafpool is Squirrelflight's half-sister.
No because the kits are Crowfeather's and Leafpool's and Ashfur never fell for Leafpool
Brambleclaw has no kits biologically, since it has been revealed that Squirrelflight did not bear him kits; instead, the kits were her sister Leafpool's. However, his adopted kits (the aforementioned kits) would be Jayfeather, Lionblaze, and Hollyleaf (presumed deceased).
No, SqurrielFlight and BrambleClaw never has kits, but SqurrielFlight takes care of her sister, LeafPool's, Kits; HollyKit, LionKit, and JayKit, Because LeafPool was a medicine cat when she had her kits in the forest with CrowFeather of WindClan.
Spoiler Alert!!!Leafpool has kits with Crowfeather of WindClan. Her kits are named Hollykit(Hollyleaf), Lionkit (Lionblaze), and Jaykit (Jayfeather)
Leafpool had 3 kits; Hollykit(leaf), Lionkit(blaze), and Jaykit(feather)
Well because Medicine Cats aren't supposed to have kits (which Leafpool did- with Crowfeather) so her sister Squirrelflight keeped the secret.
If anyone knew, she would lose her job as medicine cat.
Brambleclaw thought the kits were his because Squirrelflight passed them off as his to protect their true parentage, which was revealed later to be Leafpool and Crowfeather's kits. Squirrelflight did this to protect her sister, Leafpool, who had broken the warrior code by falling in love with Crowfeather.