There are a ton of great kid-friendly spaces online to learn more about national parks!
The National Park Service's website has a comprehensive collection of resources you can check out here: https://www.nationalparks.org/our-work/programs/npf-kids
Or watch national park videos here: https://mrnussbaum.com/usa/national-parks
National Geographic's big collection of national park books:
National Parks: A kid's guide to America's parks, monuments, and landmarks