Even something as mundane as a trip to a park becomes a free adventure with parkour, the sport of athletically navigating an urban environment. It can be attempted anywhere there are obstacles in the path. Start by challenging kids not to touch the ground while traveling from point A to point B and they will develop simple parkour moves. Professional parkour artists the Tapp Brothers have more ideas on how to get started.
Spend the day fishing and exploring nearby scenic waterways for some one-on-one bonding with a child. In addition to catching fish, this is a chance to be among wildlife and make other discoveries out in nature.
For kids who are tough and not afraid of much, pop in a scary movie, dim, the lights, and try to spook them a little. Just be careful not to screen something too scary right before bed. NPR's "Pop Culture Happy Hour" podcast inspired listeners to make suggestions online in the comments for an August episode.
Whether the model is Robin Hood or Katniss Everdeen, children will be excited to get a bow and arrow in their hands for some exercise and target shooting. Highly rated starter bow-and-arrow kits run as low as $20 at Dick's Sporting Goods, and Amazon has a variety of practice targets for less than $1.
Find a working farm that is open to the public and lend a hand for the day -- many welcome the help. Some farms charge a little (typically $20 or less per family, depending on the activity). For younger kids, think story time and a chance to explore the farm. Older kids can sign up to be a farmhand for the morning, learn the art of wood carving, check water ecosystems after sunset, learn about beekeeping, and learn to identify edible plants, plus much more, depending on the farm.
Pack a picnic lunch and take the kids out for a day of wading in a nearby park or nature preserve. Teach them to skip stones, catch tadpoles, and look for other wildlife in or near a creek.
This is especially appealing for young kids, who seem almost universally fascinated by trains and planes. Pack them up in the car and follow the tracks to find a secluded spot to park and watch trains come and go, or head to a local airfield or airport and watch the planes take off and land. It's fun during the day and even more spectacular at night.
Everything looks different at night. Grab some flashlights and head out for a nighttime walk -- maybe even turn it into a scavenger hunt by giving everyone a list of things to look for. Just be sure to wear bright clothing and reflective pieces for safety.
Test kids' balance with slacklining -- similar to tightrope walking -- at a local park, beach, or ski resort. With a slackline kit available on Amazon for less than $40, a line can be set up in a backyard or other area with strong trees or poles, close enough to the ground that a fall won't cause injury.