In kickball, if you're out, where do you go?

To the sidelines.

No, I mean like when you get hit with the ball

If you're hit with a ball and are out, then you still go to the sidelines.

https://www.digipen.edu/fileadmin/website_data/gallery/game_websites/kickball/htm/rules.htm

In kickball, if you're out, you typically go to the sidelines or a designated area called the "out zone." This is where players who are not actively playing wait until their turn comes up again. The specifics may vary depending on the rules you're playing by, but generally, once you're out, you leave the field of play to make way for the next player or team.