Buy a curriculum that uses manipulatives and teaches math using concrete language. There are many available; two good curriculums are Math U See, Mortensen Math. Research these curriculums to determine which fits your budget and your family.
Study the math lesson before presenting it to your children. Practice several of the math problems if you need. Make sure you understand the concept being taught and how to present it to your children.
Make the lesson fun and interesting. Let them see that studying math is fun. Don’t tell them that math is hard or that certain aspects of math are only for when they are older. You will be surprised at what a child can understand when their brain is not limited.
Take the lessons outside the books. Use opportunities to show how math is involved in everyday life. Use setting the table for basic counting. Use baking for fractions. Use trips for algebra.