Number Race - Kg through Grade 1 (7 - 9 years for children who are struggling with mathematics) - http://www.unicog.org/numberrace/number_race_index.html
Description - (available at the website)
The Number Race software may also be useful for prevention of math problems, or to teach number sense in kindergarten children without specific learning disabilities. The software was developed by Anna Wilson and Stanislas Dehaene, and is based on current knowledge of the brain circuits underlying numerical cognition. Details of the design of the software are published in Behavioral and Brain Functions:
Wilson, A. J., Dehaene, S., Pinel, P., Revkin, S. K., Cohen, L., & Cohen, D. (2006). Principles underlying the design of “the number race”, an adaptive computer game for remediation of dyscalculia. Behavioral and Brain Functions, 2(19).
Other math games - Ages vary
The Numberbonds game.
The Time game
The Chicks Test game.
The Dots2Track game
Allowances are mathematics too! Keep in mind also, that helping your child count, save and budget using a weekly or monthly allowance is a wonderful way to practice addition and subtracting. Setting up a simple spread-sheet for your school-aged child and keeping balances after purchases is wonderful training for learning to manage money as well as useful practice with numerical calculations. And money management is also a great way to work on self-discipline -- a very important component of executive function skill.
Tip 37 - There are many fun ways to prevent summer mathematics brain drain - from free online games for younger children to simple spread sheets for managing an allowance for older children.