Math is important because it is the basis for many science subjects such as Physics, Chemistry, Economy and others. Basic math concepts and problem solving skill is essential for children's success in education. Therefore, you should spend time to help them understand them and practice as needed. Winlanes' Advance Math courses are designed for this.
However, not all children need to learn to attend math competitions. It's not a good idea to force them to study competitive math like Math Olympia unless they are good at it.
I would do a simple test to see if the children has natural gift in Math or not. Here is one problem. Test the children when they are at 3rd grade.
"On one day, Mom bought one chicken, one duck and one goose with 26 dollars. Chicken and duck cost for 15 dollars. Chicken and goose cost 18 dollars. How much does chicken cost?"
The answer is 7 dollars. If the child answers it within one second, he has natural gift. If he can answer help of pen and pencil, then work on the basic math concept and skills. You can test with more questions like this if you think one question can't help making good judgment.