For example, a NPF’s Open Outdoors for Kids program, which affects 100,000 children nationally, is set adult such that only $10 provides one child with a outing to a inhabitant park.
Article source: https://www.huffingtonpost.com/entry/lesser-known-national-parks_us_5a3adce0e4b0b0e5a79f620c?section=us_travel