Answer:
We ran to the cars and jumped in because we hated school
Explanation:
The third option is correct because knowing the narrative voice, it is easy to assume that young people will not have any need to further elaborate on what or how they may like to say things. For them, they will just say things straightforwardly and without any other 'unnecessary' figurative language.
With that in mind, the use of the expressions such as "eager", "as a herd", "excitement", "dreaded", "long day of testing" etc will all be useless for a young child.
He would rather just get to the point and say things, even if bluntly. So, the sentence that is most likely to depict the voice of a young character is the third option.