Sunny,
Welcome to the Homeschool Forum! There is not nearly the volume of messages here that you’ll find on the open forum, but there are some wonderful people who have great resources and experiences to share. I trust you’ll be helped and encouraged.
In addition to Christy’s excellent response here, you may want to check out the comprehensive overview she posted a few years ago: The deal with homeschool science materials.
My son is in 8th grade, and he is going through Novare’s Earth Science textbook. I definitely recommend checking out Novare when your boys reach their middle school years.
I don’t have much to suggest regarding curriculum for the elementary years. My son has been in Classical Conversations since 2nd grade, and science consisted mainly of memorizing science tidbits and some simple labs. But this is the first year he is using a dedicated science textbook. We’ve lived in the DC area, so we also made lots of visits to the Natural History Museum, Air and Space Museum, National Geographic, etc. I think experiences like this and the conversations they engender can be an invaluable part of elementary science education. But I also understand the desire to have a formal curriculum to use, and I realize that not everyone lives in proximity to great museums, especially free ones.
If you have time, please add a note about your homeschooling story on the introductions thread.
Bruce