I find that OLVS and Seton are really not worth it. I do unit studies on a four year rotation with books that I already have for grades K-3...
K- I use a child science experiment book, Rainbows, Bubbles and Worms. We just do it when we have time
1-We study biology, plants, animals, humans ( like how the heart works and bones) also first aid and nutrition
2-Astronomy and space
3- Chemistry, we ended up doing a unit study on the Elements
4-Physical science, colors, motion, catapults, that sort of thing
(I start K at age 4 so this is just a basic idea, twice a week most of the time)
We do outside classes and field trips, as well.
For 5th grade and up I'm using Memoria Press' science materials. I'm considering Apologia for high school.