Miquon is a terrific introduction to math concepts for younger elementary students, as well as a good review for slightly older kids. With the e-book format you buy once, and you can print as many copies as you need. Great for a large family - or even for reviewing the occasional trouble spot.
Miquon is a creative, intuitive, child-centered approach to learning math. Children go at their own pace, and the sheets were purposely designed to look homemade so you can add in your own sheets if you need extra practice and your kids will readily accept them.
Begin with the orange book for all kids, even more advanced students. You can go through the books faster if your child already understands some of the concepts, but you'll find that there is something new to learn at pretty much every level. Miquon is non-traditional and places a great deal of emphasis on the "why" of math, so there's no drilling or rote memorization. Even Mom & Dad may find they learn a little something about math!
The teacher's manual, Lab Sheet Annotations, is recommended. You'll also want to purchase a set of math rods. This is a complete, low-cost curriculum for roughly grades 1-3 (all 6 books.)