Kids in middle and high school have pretty much aged out of the museum. If they're visiting with younger kids, send them to the Tinkering Lab or the building challenge portion of Skyline. Or, just let them loose on Navy Pier, which has some fun rides, most famously the Ferris wheel.
For kids that enjoy theater, the Chicago Shakespeare Theater on Navy Pier is excellent, and has a wide variety of plays (so still check the schedule even if Shakespeare isn't your thing).
And there are a few opportunities for fun boat rides during the summer. You can take a fast speed boat that returns back to Navy Pier or a small boat over to the museum campus if you want to let your teen explore Shedd or the Field Museum while younger kids play at the museum.
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