It's for all ages.
There are great, free nature walks Guided by expert guides which are ideal for the kids. They explained how the Canyon was formed and talk about archaeological things Through the Ages. There are many other kid related programs done well by the park ranger guides. There is lots to see and do for people of all ages, and they have a free bus which takes you to several sites throughout the Park Canyon Rim. All along the way recorded messages are played to describe what you are going to see.
No real age requirements to see. But I figure you need to be an appropriate age to do hiking.
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