Gardening
Even the littlest kids can help water. 4-5 years old and they can help to pull some weeds and pick veggies and flowers. You can make this into a great learning experience. You can incorporate teaching them about plants, the life cycle, taking care of things, working together as a team and as a family.

Nature Hikes
Take the kids to a park or the woods and point out different flowers, trees, animals, bug and more. Have them collect some leaves and make leaf rubbings, collages and laminate bookmarks with them.

Biking
Great exercise and adventure. Turn off the tv and get outside. (That is a general theme throughout all my ideas). Make sure that everyone has proper fitting helmets and that tires are in good shape. Remember to bring along plenty of water!

Picnic It.
It doesn't need to be fancy! Throw some peanut butter sandwiches and juice boxes and apples in the cooler and head out to your own front yard. Guarantee the kids will love it!

Walk
Nothing fancy required here, just take a walk. While walking, talk to your kids. About their day, their school, whatever they want. Let them know that your attention is not focused on the paper, tv, work, etc. 100% for them. They will love it, and so will you.

Camping
A bit more equipment needed here, but what a wonderful family activity. Cooking over campfires, fishing in lakes, sleeping under the stars, and should I even mention making s'mores? LOL! This is my personal favorite activity for summer.

The Zoo
I don't really need to elaborate on this, do I *grin* What kid (of any age... like me...) doesn't love the zoo. Make a family day of it.

There are so many things to do with your family in the summer, and this is obviously just a small snippet of them. My main objective for summer is to get lots of fresh air, excercise, and stay away from the tv!