I wasn't able to find anything like it online, so I thought it may be useful for the hackers out there with kids. I'm reading the book "Secrets of Mental Math", and the exercises they present are basically what this tool outputs... basic, random, arithmetic problems. So yeah, I actually created these for myself, not my kids :)

Tool: http://www.elctech.com/math/random-arithmetic-worksheets-generator

Post: http://www.elctech.com/articles/random-arithmetic-worksheets

Code: http://github.com/dylanz/Arithmetic-Sheets