Don't forget that your efforts with your child's learning are as valuable as the efforts of their teachers. You can have a huge effect on your child's learning at home, by encouraging them to try hard and do well in their studies. There are a number of things you can do at home to enhance your child's mathematical skills if they appear to be struggling with their math studies at school.
Teaching the subject to an older child may be a bit more difficult. There are many math problems out there that can be used to bring it down to their level. Using this subject in an everyday situation is a one idea. For example, tell a story that involves that child. If he goes to the store and buys a gallon of milk with a five dollar bill and the milk is only three dollars, how much money will he have left? Using word problems will help the child understand it more.