While fighting about who was supposed to watch Kiara, Pumbaa calls Timon a 'fat fat fatty', which is exactly what Matthew Broderick (Simba) called Nathan Lane (Timon) in their fight in the Broadway play 'The Producers'.
Most of the original cast reprised their roles from the original, with the notable exceptions of Rowan Atkinson who was replaced by Edward Hibbert as the voice of Zazu the Hornbill in this film and its follow-up/predecessor The Lion King 1 1/2 (2004) and Jeremy Irons, who was replaced by Jim Cummings as the voice of Scar in this film, who also voiced him in The Lion King (1994) for the last few lyrics of the song "Be Prepared".
In an earlier version, Simba was actually going to be killed by the Outlanders. It was probably not included in the film with Simba surviving the whole way through to avoid a similar tragedy from what had happened to Mufasa in the first film.
"Vitani" was originally "Shetani." It is possible to hear characters refer to her by that name. It means "Devil" in Kiswahili, however, and Disney may have thought it was inappropriate, thereby changing it to something a little less offensive. "Vitani" has no meaning in the Kiswahili language, from which most of the characters' names are drawn.
Simba's Mother Sarabi makes no appearance throughout the entire film, assuming she could've passed away after the first film, or she could've left the Pridelands. It's likely that this was done for the respect of her Voice Actor Madge Sinclair, who passed away 1 year after The Lion King (1994)'s release.
There are many similarities to the original Lion King. 'Simba' warns 'Kiara' to stay away from the out lands , just like 'Mufusa' had warned a young 'Simba'. When Kira, stumbles into the out lands she forgets her father's warning and wanders through the forbidden territory just like a young 'Simba' and 'Nala' did when they explored The Elephant Graveyard. The My Lullaby song is very similar to the 'Be Prepared' song.
The trivia items below may give away important plot points.
Originally, when Nuka died, his last words were not "I'm sorry mother, I tried", but "I'm sorry mother, I tried. I guess I finally got your attention, didn't I?" This extended scene was not included in the final release.
Originally, when Zira dies in the end, she said "No, never" when Kiara offered her help, and let go of the rocks on purpose, thus killing herself. This extended scene was not included in the final release.
There's an extended scene of Zira's Death which is nearly the exact same as the original, except after Kiara offers her help. Zira looks back down at the the river, then back at Kiara's saying "No..." Kiara gasps and Zira evily grins and finishes with "Never!" she throws herself off the rock and drowns in the river. Disney removed this scene saying it was "Too morbid for a Disney film"