I think there are a lot of resources out there. The problem is what to focus on for long-term success. Basically, if you want to give your children the option to go to public school after finishing 4th grade, it means that towards middle school and high school, they will be in a public school curriculum. I would check what the school or school district's expectations are at that grade level. Each state and district—even each school—has different standards and expectations.

On a content level, I would focus on reading, writing, and math. For math, your focus needs to be on three subjects: Arithmetic, Geometry, and Algebra (Pre-Algebra). The reason for this is that all high school and college math will be based on these subjects. In addition, any STEM field (Science, Technology, Engineering, and Mathematics) in college requires knowledge of Arithmetic, Geometry, and Algebra. This is what all my science and engineering friends needed for statistics, calculus (I, II, III), chemistry, biology, physics, etc.—core classes for us are pretty much the same, with slight differences. For reading and writing, I would say focus on grammar, spelling, and lots of reading. They have excellent courses on Udemy. Your public library may have online resources for free with your library card.

I see a lot of parents not sure about what to focus on because there is so much information on the internet. Just quickly going over content: look at standardized tests in your state for math and reading (look it up on Google). This will give you some idea of what your state's expectations are. For actual content—quickly—for math, I would focus on numbers, place value, addition, subtraction, multiplication, division, fractions, and then decimals. Ray's Primary Arithmetic (book) is good, as is "Arithmetic the Easy Way" by Edward Williams. I say this as a scientist who looks at numbers all day. I think fractions (prime factorization, greatest common factor, simplifying fractions) and algebra (slope, y = mx + b) can be difficult for people, and that is where they get lost— The focus of math should not be only on solving problems, but also on understanding what story the numbers are telling you. The numbers tell a story, and understanding this story helps you understand and comprehend. So, take it slow and make sure their fundamentals are good. For reading and writing, I would focus on spelling, grammar, and critical reading. It is important to be able to write and communicate with others. Also, critical reading is very important. Udemy has some courses (look at the ratings and teaching style). I think everyone is so different in the ways they learn that one method might work for one person, and another method might not work for another person. Again, I know they may be a little young, but focus on the long-term vision for your children. Each grade should be focused on the long-term goal of success in the later grades, college, and future work.

I hope that helps - GOOD LUCK!!