Hi,
We should at least attend if not participate to EduTech (24-25th of March) and Open Education Day (24th of April - saturday).
I would present it this way:
Talking of GCompris as an educational Swiss knife that can be used in different environments, for different purposes, and light enough to run on a maximum of hardware.
I would present it thought a classic child day and show how it can help learning throughout the day.
At school where teachers could use it to teach most of the competences to be taught via a pool of more than 150 activities, I would then present briefly the different domains and show some of the activities.
Tell that GCompris in class can help discovering a concept as it corrects straight away. Explain that this feature allows active and reflective learning (which is difficult to obtain when working in classic condition) because of the automatic correction.
GCompris in class is also a training tool that once a concept is understood can be used to train competences.
Running on low hardware (mum and dad's 6 year old telephone, raspberry-pi) GCompris allows with a minimum cost to provide training tool for homework to consolidate what has been learned at school.

All this is now possible since version 1.0 as GCompris offers dedicated exercises for each age group between 2 and 10, allowing teachers and pupils to choose the level of difficulty they want to work on.
There I would present "falling dice" that allows to train counting from 3 to 9, explaining how it teaches the concept for ages between 2 and 5 (showing activity config screen).
Then for the older "Give Tux his change" that trains subtraction for the age of 6 to the age of 10.

Having presented GCompris as a school tool, it is also a tool that can simply be used by children to discover knowledge and comeptences on their own while having fun. If you can ever take the time to look at children discovering on their own how to open a canal lock (here show video of canal lock in background), trying, failing, achieving and explaining you how they did, you will see how much happiness this can bring to him.