The number of resources available online is vast. Here are just a handful of suggestions to get you started.

 


The Art of Problem Solving

online courses for math kids, a bookstore, forum, Wiki, tutorials, and more


Cut the Knot

a repository of mathematics miscellany and puzzles

Numberphile

“Videos about Numbers and Stuff” 


Vi Hart Videos

the YouTube channel of a "recreational mathematician" 


Thinking Mathematics! 

a collection of videos, essays, puzzles, and more from James Tanton