There was a time that the United States of America had some of the highest mathematic scores in the world for students in grades k through 12. A lot has changes since those days, and in order to help children get back on the path to being good mathematical students parents need to play an important role.
Parents can assist with developing a lot of the fundamental skills needed for children to succeed in math when they attend school. Parents can do things that will support the schools and hopefully the schools will do the rest.
Get in the Kitchen! I was very hesitant for a while with my son when it came to the kitchen. I worried about the GIANT mess that would be left when he was done "helping". You don't even have to take on the entire project with them! You can start small and let your child help with measuring certain ingredients. You can modify the difficulty of the 'lesson' by talking about the different kinds of measuring cups and seeing what other measurements can also add up to equal one cup, etc.
For example, all children should learn their multiplication tables by the third grade. They should be able to repeat them, verbally, without using a calculator. Children in elementary school who rely on the calculator for the answers are creating math deficiencies, which could have a negative impact on their math development.