Prince Caspian looks at the four children and sees that they are young and alone. How can they go up against Miraz’s army? (David is young and goes to fight Goliath with only a sling and stones.)
Lucy saw Aslan but the other children didn’t. She should have followed him even though the others wouldn’t but she gave in to their influence and bad consequences resulted. Later she admitted to Aslan that she was wrong and he forgave her. (Come, follow Me. God forgives us but we often have to suffer the consequences of our sins.)
Edward, who had followed the White Witch in the first movie and was redeemed and forgiven by Aslan, was one of the heroes in the second movie. (Who was forgiven much, loves much. Jesus came to give us new life.)
The battle = the necessity to resist evil, even to the point of death.
Caspian and his people were not Narnian by ancestry but Aslan welcomes him and those of his people who are willing to remain in peace to be part of Narnia. (The gentiles are accepted into the kingdom.)
At the end, the children have to go back into their own world. (We can’t hold on to our experiences of God. Sometimes we have to continue with our daily life and just live by faith.)
Peter and Susan are told they won’t return to Narnia because they are growing up and must encounter Aslan in their own world, (We have to become adults in the faith and this may involve sacrifices.)