This is the 11585th most frequent French word.
réjouir
"Réjouir" means "to delight" or "to make happy."
Here, "réjouir" is used reflexively to indicate that the children are experiencing joy or happiness about the idea of the upcoming vacation.
Les enfants se réjouissent à l'idée de partir en vacances.
The children rejoice at the idea of going on vacation.
In this sentence, "réjouir" is used transitively to express the act of causing someone to feel joy or delight. The movie is the subject that fails to evoke this feeling in the speaker.
Ce film n'a pas réussi à me réjouir.
This movie did not manage to delight me.
In this context, "réjouir" is employed transitively to describe Jean's action aimed at creating happiness or delight in his friends through organizing a surprise party.