Doesn't MIT's Scratch [1] accomplish this? I was going to default to this. I'm wondering how much reading, writing and math my kids need to have before starting this. Reading complex sentences and addition and multiplication of single digits? (Wrong thread to get started on what EWD [2] thinks on this...)

[1] http://scratch.mit.edu

[2] http://www.cs.utexas.edu/users/EWD/transcriptions/EWD10xx/EW...