The Lion King II: Simba's Pride

The animals of the Pridelands gather to witness the celebration of the newborn cub, Kiara, daughter and firstborn offspring of King Simba and Queen Nala. Simba's father, Mufasa, proudly watches over the ceremony from the Heavens above. As she grows older, Kiara becomes annoyed with her father's overprotective parenting. Simba assigns Timon and Pumbaa to follow her. Kiara ignores her father's warning and the duo's attention and enters the "Outlands," where she meets Kovu, a cub who was chosen by Simba's uncle Scar to be his heir. When Kovu retaliates to Kiara's playing, Simba confronts the young cub just as Zira, Kovu's mother, confronts him. Zira reminds Simba of how he exiled her and the other Outsiders, and she reveals that she selected Kovu to be Scar's successor.
After returning to the Pride Lands, Simba sends Nala and the rest of the pride back to Pride Rock while he lectures Kiara about the danger posed by the Outsiders. Simba then tells her that they are a part of each other. Meanwhile in the Outlands, Zira reminds Kovu that Simba killed Scar and exiled the lions who respect him. Kovu explains that he does not think it is so bad to have Kiara as his good friend, but Zira realizes she can use Kovu's friendship with Kiara to seek revenge on Simba.
Several years later, Kiara begins her first solo hunt, but Simba has Timon and Pumbaa follow her in secret, causing her to hunt away from the Pride Lands. As part of Zira's plan, Kovu's siblings Nuka and Vitani trap Kiara in a fire, allowing Kovu to rescue her. Unable to thank the young rogue, Simba is forced to accept Kovu's asylum since Kovu rescued Kiara. Later that night, Simba has a nightmare about attempting to save Mufasa from falling into the stampede but is stopped by Scar who then morphs into Kovu and throws Simba off the cliff to his death.
The next day, Kovu contemplates attacking Simba as he was instructed to, but he teaches Kiara how to hunt instead and eventually realizes his feelings for her. Later, Kiara and Kovu stargaze where they talk about the Great Kings of the Past and Kovu wonders if there is a darkness in him like there was in Scar. Simba watches the two from afar and Nala convinces him to give Kovu a chance. Kovu attempts to reveal his mission to Kiara, but Rafiki interrupts and leads them to the jungle, where he introduces them to "upendi", which means love in Swahili. The two lions fall in love. That night, Simba allows Kovu to sleep inside Pride Rock with the rest of the pride, but Vitani tells Zira about Kovu's failure to kill Simba.
The next day, Kovu wants to reveal his mission to Kiara, but Simba takes him around the Pride Lands and tells him the real story of Scar. They fall into Zira's trap and the Outsiders attack Simba. Kovu attempts to intervene, but Vitani injures him. Nuka attempts to kill Simba, but Simba flees and Nuka is killed. Zira scratches Kovu for his brother's death, causing him to turn on her. Kovu attempts to plead Simba for his forgiveness, but is exiled. Kiara makes Simba realize that he is acting irrationally, and flees to find Kovu. The two lions later find each other and profess their love. Kovu wants to start a pride of his own with Kiara, but she tells him to return to the Pride Lands and reunite their prides.
The Outsiders and Pridelanders fight, but Kovu and Kiara intervene and tell Zira and Simba to stop fighting. Vitani and the Outsiders side with the Pridelanders. Zira attempts to kill Simba, but Kiara pushes her over a cliff, dangling over a storm-swollen river. Kiara offers her help, but Zira refuses and falls to her death. Rescuing Kiara, Simba reconciles with the Outsiders and Kovu, allowing them to rejoin the Pride Lands. Simba accepts Kovu as his son-in-law and the future king and Kiara the future queen. Simba looks up at the sky to hear the approval of his father, who says he is proud of him.

Question: Who is Simba and Nala's firstborn offspring?
Answer: Kiara.