Muireann,
counting sections of an image is a great way to use estimation to gather data.
If your image includes a swathe of the Milky Way, this can lead to an purposeful discussion about how stars are not evenly distributed around us. For a further step, you could ask the children if it would be possible to tell where the Sun and Earth are in the Milky Way by looking at the star counts in different directions.
The image from Lots and Lots of Stars could work, or this image from ESO called GigaGalaxy Zoom and here.
