Teenagers will be teenagers. I'm one, and I argue and fight with my siblings. But my parents never allow me to run my mouth like that in front of somebody. I may be too old for it, but my grandma would either pop me to stun my jaw, and my dad would spank me. It's embarrassing, so I learned to shut up. XD
I don't think it's so much OOC as it is character development. Nala was extremely rude to Zazu, so why would it differ to a cub she thinks is 'strange'? Also, many kids tone down when they become adults, I'm sure Sarafina learned her lesson about bullying when she was with that rogue pride.
"You know your mother is out hunting, Taka. And your father is teaching your brother how to become a good king..." "And why am I not allowed to join them?" "When you grow a little bit more I am sure you'll be able to join them too" "Pff, if he ever grows, this tiny, weak thing!" "Your mother asked me to show you the Pridelands" I think that's what you mean by pleased. Am I right?