Binary Addition

I would like to move towards SBG for various basic topics in my Digital Electronics class next year. To that end, I will spend this summer creating and/or finding online practice tools for my students to hone their skills. 

One of the topics they learn is Binary Addition. After searching for "just the thing" online and coming up short, I created a Scratch program for them:
 

I think I'll leave it as such, but if you have any suggestions for improvement that can easily be done by a summer teacher, thanks for sharing.

Also, I had originally created this program with Java with the intention of making an applet to put on our school website. This turned out to be a pain full of "security issues" ... "bad!" .... "don't even think you can open or share this applet". Don't know if I'm doing something wrong, or if that's the way of applets these days, and I have to pay money or some such to be able to have that message not come up. Does anyone know?