This would be the lion king 3. Kopa is the first born of Simba. Kopa's life is pretty normal at first but suddenly his life takes a turn for the worst. View Kopa's journey here.
This is about when Simba and Nala were growing up as cubs. What other adventures did they have beside their visit to the elephant graveyard? This story stars when they first meet and tells about all of the adventures that they had as cubs.