Have a Faith Race

Have a route set up for blindfolded people to be lead around in an exercise of faith and trust. Have some 'dangerous' parts to the course, like puddles or bushes, that will make the blindfolded person hesitant to run near such things quickly without being able to see for themselves. The faster the course is completed, especially if attempted again, shows growing faith in their guide.
Maybe then try the course blindfolded without a guide - see how much slower it is when you try and do things on your own without following your guide...

Fly a Boomerang

Marvel at the laws of physics by throwing and catching a boomerang. Create your own design, keeping to the 'wing' shapes required for it to actually fly, or purchase a proper returning design, and research how to throw them (there's a few angles to get right but it's not too hard once you catch on). Marvel at how it can be thrown one direction and by slicing through the air it can return (with some practice). Get a few boomerangs and friends together in a large field and have fun trying to get consecutive catches together and even learning the flying pattern so well to be able to perform trick catches.

Guess the Scent of Flowers

Have someone test you on your flower scent knowledge. Blindfolded, have someone bring you, or lead you to, a variety of flowers and guess what they are by smelling their scent alone.
You could allow touch too for 'half points'.
Take turns, and also repeat and see if people do better the second time.

Play Nature Photo Detective

Have someone secretly take a photo of nature somewhere in the yard or park and get everyone else to try and find that piece of nature by using only clues in the photo. This can be made easy or very hard depending on what you include in the photo.

Make a Cryptic Treasure Hunt

Make up a cryptic treasure hunt where there are clues at each stop for the next location - until you get to the the final treasure. If played outside, clues can force people to observe the nature around them closely, or if played inside the clues could consist of Bible texts that mention a household item.
Three different examples: Look behind the deciduous/evergreen tree. I'm pink and Bees like me. Luke 11:25 

Play Under a Sprinkler

Hot day? Have a play out under a sprinkler - kids AND parents! Of course, adhere to local water restrictions and remember to be 'sun smart'.

Play Hide and Seek

Play hide and seek out in nature. Adam and Eve were the first people to ever play hide and seek. God, like all good fathers, played along for a little while before finding them. (Gen 3:8-9)

Catch a Leaf

Use your hands, butterfly nets or any thing else you can think of to try and catch some falling leaves from a large tree on a windy day.

Skim Some Stones

Find a river or lake with some small, smooth stones you can skim across the water. See how many 'skips' you can do or how far a stone travels or how accurately you can skip your stone to an object.
A fun variation of this challenge is throwing 'skimming stones' straight up so they land in the water via the thin side and make an amazing 'chilkk' sound - with no splash.

Play I Spy

Play I spy with my little eye, something beginning with . . .
Set the rule that objects must have been created by God or found in the Bible.

Blow Dandelions

There is several challenges you can take on with the amazing design of dandelion seeds.

1. Try and blow them all off with the least amount of blows.
2. Try and blow them all off in the most amount of blows - but each blow MUST dislodge some seeds.
3. See how far you can blow the seeds in one blow.
4. See how far you can blow the seeds by continuing to blow them up in the air until they hit the ground.
5. See how many dandelion flowers/seeds you can find that are in differing stages of their growth
6. Find the biggest and smallest flower/seeds that you can.
7. See how many you can pick - guess how many you think you have before you count them at the end.
8. Use a magnifying glass to closely observe the flower/seeds.

Look for Biblical Cloud Formations

Watch the cloud formations and look for shapes that:

1. were created by God (other than a just a 'cloud') - 1 point
2. look like an object mentioned specifically in the Bible - 2 points
3. look like a scene from an event in the Bible - 5 points

Others must be able to 'see' your discovery before you can claim the points.