If you already have a Droid Inventor Kit, you can code with your Droid! All you need to do is update your version of your Droid Inventor app to include the new coding missions. You should be able to do this from the App Store or Google play.
Once your app is updated, simply update to the "Missions" section by clicking "Begin Missions" from the home screen.
If you scroll through the missions, you'll see special coding missions have been added.
Once you complete the base missions, it will unlock the coding missions and you can try your hand at coding with the Droid.