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 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.
YES. in one of the books, Ashfur tries to kill the Three but Squirrelflight says that they aren't really her kits. Later, the Three unravel the web of mysteries and find out who their true parents are.
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.