A blanket, a day with some fluffy clouds, the book, "It Looked Like Spilt Milk"
Lie on your backs and gaze at the sky. Babies will enjoy the sensations of the wind, leaves rustling, and the connection with the adult. Toddlers and preschoolers will enjoy naming the clouds by what they look like. You may need to start this by pointing out ears, noses, wings, etc. School-age children may become curious about why there are so many different shapes, why they change, where do they go when they disappear, etc. To prepare for these questions or to research after a gazing session go to www.window.ucar.edu.
Point out all you see and hear while lying quietly - Birds, airplanes, bugs, colors,...