Most of the questions on MSE about educational resources are for high school. At least I haven't found questions which deals with sites on very elementary mathematics.
I will be grateful if someone provides me with list of educational resources for kids - e.g. of the level of kindergarten, primary school and junior high school.
If you think that this question is not for MSE, tell me were is it appropriate to ask?
Though not a direct answer to your question, another resource you may be able to use is a university sponsored Math Circle program. They really are amazing and I am extremely jealous of those kids (I wish I got to go to a Math Circle when I was their age!). If you're not familiar with what it is, it's basically a program where your kids can go and learn mathematics they wouldn't normally be exposed to in school, with peers of their age.
To give you an example, at UCLA (where I attend) the fifth grade age group learned basic abstract algebra, cryptography, and fundamentals of proofs.
Check your local schools out! Math Circle Main Website
Here are some things I found in a few minutes. I'm also including what seemed to be the best google search among those I tried.
Google search for “elementary school” mathematics resources links
Math Archives: K-12 Teaching Materials
Awesome Library: Elementary School Math
Ask Dr. Math: Elementary Archive
Ask Dr. Math: Middle School Archive
WGBH has launched an all-new bilingual Web site and curriculum for PEEP and the Big Wide World, the Emmy Award-winning preschool science and math series for 3-5 year olds.
TenMarks Education has a professional development, preparatory, and in-class resource for teachers. The program focuses on grades 2-6, with instructional resources for 12 core standards available at no cost to educators. It's called TenMarks Math Teach.
Glean - An excellent site for fiding educational videos and lessons on math and science.
