I believe there is something imporant about kids engaging with the outdoors. For my kids there something "magical" about rocks and water. As difficult as it sometimes is to get my kids outdside, once we find that perfect combination of rocks and water something "clicks." What is it for your kids?
My older son will throw rocks in water for hours on end and my newborn likes to feel the grass in his hands (and then it goes straight to his mouth !). Watching clouds, comparing the radar of the storm and what's happening outside when a storm rolls in, and playing baseball by the Lake are all part of our everyday.
Any time we are heading outside we refer to it as 'going on an adventure' and we make sure that we take all the time our kids need to absorb their surroundings and focus on what interests them. Sometimes that means we don't get very far but it's really rewarding when they ask if they can 'go on an adventure'!