The new App Inventor by MIT uses the same building block principle for developing Android apps as their older, and very popular, sister Scratch by MIT. They say:
App Inventor lets you develop applications for Android phones using a web browser and either a connected phone or emulator. The App Inventor servers store your work and help you keep track of your projects.
I haven’t tried it myself, but it looks like a great way for younger kids to develop and test simple mobile apps without much hassle!