Pack a picnic and a camera and take the kiddos on a hike. Make a list of things for the kids to collect and/or take pictures of on their hike.
For example:
Things to Collect:
Cool rock
Pine cone
Leaf
Stick
Things to take pictures of:
Black Bird
Blue Bird
stream
footprint
insect
mushrooms
Etc.
You can even assign yourselves new names and pretend that you're explorers (My girls like to be Dora and Boots...and then they assign my husband and I the names 'Swiper' and 'Diego')
Find a nice spot to sit and eat your lunch, and talk about the interesting things you've discovered.
