It is one of those subjects that will cause people to question how well it can be done in a home environment. Recently I read this blog entry by Susan Wise Bauer on the subject of science, labs and school.
For my kids right now science is all about exploring, playing and getting to know the natural world. We do plenty of nature walks, and discuss how the landscape changes each season, what animals are around, those kinds of things. When the mood strikes us we do play with chemistry kits and do experiments. My 7yo told me the other day that many of the things we use in the kitchen can be very useful in making mixtures that cause reactions.
Children have a natural curiosity about how the world works, why things are the way they are, and they want to learn. A textbook and worksheets isn't necessarily going to foster that and might even kill it to a degree.
As we go alone certain things catch their attention and they want to devote more time to learning. Geology caught their attention one day when they dug up an unusual rock in the yard. They checked out some rock and mineral field guides from the library and spent a couple weeks outside gathering rocks and working hard to identify them. While doing their investigations they learned the different ways to identify rocks, rock classification.
Lately for the younger two the interest has been birds. They found an encyclopedia about birds in North America and spent many hours outdoors identifying birds in our yard, and taking a count of each type.
My 9yo has rediscovered an interest in paleontology and checked out a recently written book about dinosaurs. Within that book he is learning about mass extinctions, math concepts, geology and gaining some familiarity with Latin.
I really love seeing how much the kids learn through their own studies and simply by following the course their curiosity takes them.