Use things around the house that they already know and love! : My son has a HUGE adoration for his Thomas Trains... he can tell you every single trains name, number and color. When we started working on recognizing numbers and colors, I tried to use posters, games, workbooks, etc that would help him learn to recognize them... all to no avail! One day, we were playing with his trains, and HE asked me what number one of the trains was. Bells went off in my head and I realized that I could cater his natural curiosity about his beloved trains, and still be 'teaching' him to recognize numbers at the same time!
Also, when the child is in the second or third grade and their child can't add simple two digit numbers, it is up to the parent to make sure that their child gets the extra help needed to become successful. Parents cannot wait on the school every time their child has an academic deficiency. Part of being a good parent is making sure that your child functions at the correct grade level throughout their academic career.
The classes can be taught at the various colleges or universities in the local area. This is a community outreach for the colleges and universities, but children will develop social and academic skills that will carry over to their classroom and on to adulthood.
Another strategy involves allowing your child to spend some time on a computer playing math games. The computer can be a wonderful resource that supports math and other subject area skills. Software is available that will measure a child's math skill level.