In this video a small group of children are using the Hot Spots application to identify the names of different musical instruments. The application allows the user to move word labels (you see in the first part for the video) and also pictures.

In my experience four children is the maximum for junior children to work together. Ideally it would be less because you have to divide the space, the screen real estate and the number of questions by your users. Too many people around it and engagement dwindles.