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.
If you find that your child is still really struggling after a number of efforts at home, there is one final thing you can do. The option of hiring a personal tutor is becoming more popular throughout the States. Personal tutors can help your child get to grips with things they never used to understand and provide a more personal form of education. The personal tutor will become more of a friend to your child, than a teacher, meaning the teaching style will be vastly different to that of their school. It's one of the best ways of helping a struggling child.