I have yet another theory on Zira's little family over there.  Sorry if there's many other topics/articles on this, but anyways...  Here are my theories:

Nuka, Swahili meaning: Smelly

TLK hints at Nuka's parentage, such as in the line muttered by Nuka: "Kovu Kovu Kovu.  Scar wasn't even his father."  This suggests that Scar was Nuka's father, as Nuka seems to consider himself more deserving when it comes to taking the throne, possibly because of his own lineage.  So, I believe, as do my other TLK fans, Scar sired Nuka.  As for his mother, the most popular candidate is Zira, which I agree with.  Nuka refers multiple times to Zira as "mother," suggesting that he is indeed her son, and Zira shows deep affection for him as he is dying, and refers to him as "my baby."

Therefore, Scar+Zira=Nuka

Vitani, Swahili meaning: Battle (Original name said to be Shetani, which means "Satan" in Swahili)

There are virtually no hints in TLK2 to who Vitani's parents may be.  However, if we consider her unique appearance, we might be able to make a reasonable guess.  Let's take into account Vitani's yellow-golden-blonde coloring, dark eye 'rims', and a backwards chin-tuft, as well as the obvious fact that she resembles an Outsider.  Now, the rarest feature about her is probably her bright blue-purple eyes, if we set aside her signature head-tuft.  Who else do we know who has blue eyes?  First lion that comes to mind: NALA!  But, we can't forget her mother, Sarafina, as well.  So here's my theory for Vitani's parentage:  Scar, being king at the time, could take whatever mate he wished, and after siring Nuka, realized Zira could not provide him a suitable heir.  He mated with Sarafina, and she bore him Vitani.  However, in Scar's eyes, Vitani could not be ruler because she was female.  Sarafina, wanting nothing to do with Scar or the daughter he had given her, abandoned Vitani, who was taken in by Zira.  So you see?  Timing works out (Vitani is closer to Kovu/Kiara's generation than Nala's), appearance checks (blue eyes, backwards chin-tuft, nose color, and blonde fur from Sarafina, and Outsider appearance, nose shape, puffy cheeks, dark eye 'rims', and possibly head-tuft from Scar), parental age works (Sarafina and Scar are more-or-less in the same generation, though I'm not sure how lions view the whole age thing), and the Zira-as-a-foster-mother thing fits (Vitani is taken with Zira to the Outlands after the exile by Simba).  Though Vitani does refer to Zira as "mother," this would most likely be because she was raised by Zira.  Also, this explains the rivalry between Nala and Vitani--as this would make the two half-sisters--in TLK2, in which Vitani taunts Nala by saying, "Where's your pretty daughter, Nala?"  Nala responds by angrily muttering "Vitani!" and the two proceed to fight. 

Therefore, Scar+Sarafina=Vitani

Kovu, Swahili meaning: Scar

The only thing we know about Kovu is that his father was not Scar, but nevertheless was selected to be his heir.  Most likely, neither of Kovu's parents appeared in any of the films (though I believe Kovu's father to be Chumvi due to similar coloring--his mother remains unknown.  Though some believe her to be Zira, I think think is unlikely due to 1. the fact that there are zero indications of this in the movies and 2. the age difference between Zira and Chumvi.  However, Kovu's mother most likely was an Outsider, giving him his partial Outlander appeareance.)  My theory is, for whatever reason, Kovu was abandoned as a cub very near the end of Scar's reign, and Scar, desperate for an heir, selected the healthiest cub he could find and proclaimed him his successor, naming him [in Swahili] after himself, and giving him to Zira to raise.  Kovu was most likely very young at the time of the Outsider's exile to the Outlands.

Therefore, Chumvi+???=Kovu