Sometimes the best way to teach a subjct is to lay some groundrules and then let students actually "do" what they're studying. This is especially true of science, a study predicated on activity, experimentation and the observation of physical properties. It's also one of the best ways to get kids interested in science in the first place.
If he hadn't stood atop the Tower of Pisa dropping things off the edge, Galileo would never have made his observation that objects of any weight fall at the same rate in a vacuum. Archimedes had to get in the tub to discover that it is volume that displaces water. And the only way Newton could discover the calculus was by scribbling numbers on pieces of paper.
Your kid probably isn't the next Einstein, but that doesn't mean he shouldn't learn as much about science as possible, or that he should do so with his hands tied behind his back. The problem with a lot of science textbooks is that they emphasize book knowledge without taking into account the hands-on nature of science and science learning. Observation is often touted as an essential part of the science process, but rarely is it enforced in they typical school curriculum.
Science resources can change all that. There are plenty of fact-based books (particularly those from Usborne) that pair facts with vivid illustrations, and those are fun for rainy days—kids are a lot better at acquiring and retaining raw information than we often give them credit for. But those are just a place to start; the options are limitless.
One of the best sorts of science resource are books filled with experiments. Whether it's Explorabook from Klutz Press which focuses on fun activities and includes everything you need to complete them, or Vicki Cobb's Bet You Can! experiments using household items, or the more advanced Science for Every Kid books by Janice VanCleave, you aren't likely to run out of options.
Astronomy is more observation-oriented, and we offer plenty of books on that topic, too. The Stars by H.A. Rey is a now-classic guide to the night sky for beginners, while Starry Messenger explains some of the basic tenets of modern astronomy through the (detailed and beautifully illustrated) life of Galileo Galilei. Isaac Asimov has written a number of books on space science, as has Seymour Simon.
Just letting your kids outside with notebooks and maybe a magnifying glass is as good as any book for helping them develop a love of nature and nature study, though manuals to help them identify plants, animals, rocks, etc. is a good idea. One of our favorite such books is the Handbook of Nature Study by Anna Botsford Comstock.
Keeping a well-stocked chemistry lab is a good idea for older students. Many experiments require chemicals, ingredients and equipment you aren't likely to just have lying around, so you'll need to be intentional about keeping a lot of those things stocked. Field trips are always a good idea as well, whether to a local laboratory, observatory, zoo, factory, or anywhere else that strikes your kids' fancy and has educational potential.
Whatever else you do, keep an open mind while guiding your kids' science education. The beauty of God's world and the excitement of learning about it should always be kept in view; whatever difficulty there is in physics, biology or chemistry should be met head on but not dwelt on or made cause for discouragement. Have fun, and don't restrict your science time to reading stuff—take time to actually do science, and you might find along with your children that it isn't such a bad thing to study after all.