Ok, here we go...
1. Visit the education supply store and choose some kind of workbook. This will form the backbone of your study. Personally, I'm a fan of the ScienceWorks series published by Evan Moor. They offer a good mix of worksheets and activities. Visit the Grades K-5 page for some links (look under "Supplemental").
2. You can also get some supplementary books from the library for other experiments and activity ideas. You can also check out short books on various topics to read aloud. I think the "True Book" series is pretty well done for Grades 1-3.
3. Incorporate reading/literature into the study by reading selected books from the Magic Tree House series that relate to the topic you're studying. These are available at any public library. Examples:
- Dinosaurs Before Dark (book 1)
- Midnight on the Moon (book 8)
- Earthquake in the Early Morning (book 24)
4. Discuss, discuss, discuss. I can't emphasize enough how important this step is. I constantly review what we've been learning, ask the girls questions and explain concepts repeatedly. This is also the point where you can bring in some discussion about biblical integration. At this age, don't worry about the whole evolution issue. It usually just flies right over their heads and kids won't get uptight about it if we don't. Just try to focus on the positive: "Hey! Isn't that cool? Look what God did! Let's learn more about it." There will be time enough for addressing evolution later.
5. Field trips. If you're doing a unit on dinosaurs, how about a trip the Natural History museum? A study on basic astronomy would warrant a trip to the local observatory.
Hope that helps.