Student Tutor's 2013 top ten list of free math resources for children K-12 ranks Patrick JMT, Khan Academy and Arcademics as the best three available. Patrick JMT is entirely dedicated to math, while Khan Academy and Arcademics contain resources for other disciplines as well.
Patrick JMT is for third grade and up and includes everything from basic arithmetic to calculus and statistics. All lessons are in video tutorial format and listed under broad categories, such as arithmetic or linear algebra; however, they offer very specific lessons which are short and easy to understand. Children can select tutorials from the home page or use the search box to locate desired topics.
Khan Academy includes math lessons for K-12 and beyond. Lessons for K-8 are broken down by grade while high school and beyond offers everything from algebra basics to integral calculus. Children of all ages can instead focus on foundations of early math, arithmetic, pre-algebra or basic geometry.
The vibrant Arcademics site is for the younger children of K-6 and strives to make learning engaging and fun. Kids can learn the basics while playing Alien Addition or Sailboat Subtraction. Older children can practice algebra with Swimming Otters or Dirt Bike Proportions.