Насколько я понял тут надо составить кастомные предложения. Одно вытекает из другого.
If they open the box they will find a map.
If they follow the map they will reach the castle.
If they reach a castle they will meet a princess.
If they meet a princess she will give them a(любая вещь, которая может помочь забраться на дерево) ladder.
If they climb the tree they will look in the nest.
If they look in the nest they will see an egg.
If they see an egg they will drop it.
If they drop an egg the monster will appear.
If monster catches them they will get 3 stars.