Penjee.com is the best way to teach kids python. It's a fun engaging way to make a transition that kids typically struggle with: how to transition from a drag and drop type of coding like Alice to the daunting world of "real programming language" like Python.
Penjee's choice of Python is perfect for beginners but what really sets Penjee apart from other sites is its learning environment. The site's videos are easy to understand, and the site's tutorials explain concepts in a friendly engaging way! (See Youtube Video below)
The student challenges are scaffolded and differentiated. In short, student's are able to try to achieve the same learning goal multiple times through "mike and ike"/ "jen and jill" versions of the same assignment (more here).