Check out https://scratch.mit.edu/.
I've run workshops for students of that age group to learn scratch, so I second this, but will add some advice echoing something similar to @pedal stache... Consider doing some offline things as well that help with the logic/rules aspect (check out scratch cards as one type of support - but I think some other logic generating activities as well are useful), since at that age, the interaction with something more Kinesthetic tends to help keep up the level of interest.
Believe it or not, Minecraft is another option. Learning how to do customization there can draw in folks who heavily enjoy it. Younger son of one friend has totally been into this for a while (just turned 10).
A few other ideas: If you're ready to get into a little bit of hardware as well, check out
http://makeymakey.com/ ... it can be used to do some fun projects around carrot chimes, et al. This is great because they are doing something that is less abstract than on a computer - it's a physical thing they can interact with...
Starting at 9, you can also consider First Lego League, where they will learn to program (and build a robot). That season is wrapping up now, and the teams usually fill very fast, so you will want to start looking around next Spring. Just after the high school teams finish in April, you should be serious about finding a team for the fall. Much of the team creation is finished in June/July.
Other local companies where I am have also used Sphero:
http://www.sphero.com/sphero to do demonstrations, since it can be controlled from a tablet, which seems to make it more accessible for some students. Build a maze with legos (or left over duplos) and navigate it is a good intro to logic.