GCompris is a very famous education programs for kids (heck, it even has electronics circuits!) and has attracted lot of contributors in the past.
It was announced that GCompris is moving to Qt/QML to make it easy to provide support on mobile/tablet platforms. Read the announcement at http://osdir.com/ml/general/2014-02/msg15205.html
where the author is asking for help from people in contributing to the new Qt version. I think it is a very nice opportunity for those of you who want to contribute to FOSS because-
* The app is kinda fun on its own
* It is very famous and widely used
* While implementing the new version, you can always run the old version and get a feel of what you're looking for
Also, there is a good chance that GCompris will be an organization in GSoC (or as it is a Qt project, it might become a part of KDE).
If you are interested, hop to http://gcompris.net/wiki/Developer%27s_corner
and contact them mailing list, IRC. And as always, you can ask your questions here as well!