They can start with asking simple math questions and going on to harder questions, as the child gets older. Parents should continually ask children mathematical computation questions and give positive feedback when they respond. Children love to receive positive feedback and that encourages continues growth.
Anything less could cause children to suffer a tremendous loss. The teacher that parents should be trusting to teach their child math is a person that will challenge their child regardless of their age. In addition to the challenges, the teacher should encourage children to try hard. Children need to know that their teacher cares about them and is not just trying to give them a lot of hard work.
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.
Once you lay the foundation with a strong trading plan; an understanding of the interrelationship among money management, technical analysis, and risk management; plus a knowledge of the difference between speculation and gambling, you will find that you can have an enjoyable trading experience, whether you are winning or losing.