My recommendation for a science curriculum K-12 is Apologia. It’s solid, complete, interesting, and can be used well and easily in a homeschool setting. The elementary level books (K-6) can be completed by teaching science twice a week with your children all working together. Here are some links to get you started. The whole website is very helpful.
The FAQ video does a good job answering the basics (scroll to the bottom of the page for the video):
Scope and Sequence for Middle School-High School: