To add on to what JB said, I like the Khan Academy videos - though the kids seem most interested in them when it's not their first introduction to the topic - and we have some Singapore Math workbooks. I'm starting to think we need the Singapore textbooks as well, we need some actual teaching that they're not getting (they hate for me to teach them anything. what does mom know...)
The least math-y of my three oldest kids, ds6, recently read "Life of Fred - Fractions." I don't think he actually learned any math (he refused to even try the problems at the end of the chapters, even with my help) but he loved the book so much that he walked around with it for days, and he has asked for more from the series. I'm trying to pry it away from him so his more mathy siblings can read it; hopefully they'll learn something.
As for how else to approach afterschooling, I don't really know. I may be talking to their teachers sometime soon but I haven't figured out what I'm going to say.
