One great way to teach it is by using math worksheets. One could make worksheets that are fun for children to complete. Adding graphics such as fruit and candy and having the children add them up will open their minds to it and have them learning in a fun way. Also, the sense of accomplishment the child has after completing the math worksheet correctly will encourage him to continue learning the subject.
Combine math with reading _ There are quite a few nice children's books out there about math and who does not like a deal. Imagine it's a 2 for 1 deal you are getting, with the opportunity for your kid to enjoy reading and math at the same time. The Sir Cumference series comes to mind with its attractive illustrations and adventures. Less than Zero is another. It gives a good introduction to the concept of negative numbers. Also One Hundred Hungry Ants appeals to kids too. Well who doesn't love bugs? Check out online stores where you can read reviews but remember to ensure that the reading level is not more advanced that necessary to get the math concepts across. If that is the case that will just take the fun out of it and make your children frustrated.