Oisín,
since phases of the Moon appears in second level not primary, looking at the phenomena with a view to light and shadow is the best way to examine it.
From doing a similar activity with secondary students, there is a lot to it, and children need to take the time to explore. I would suggest starting with New Moon and Full Moon, and if you can, go outside with Moon balls (styrofoam on a stick) and let the actual Sun light up the Moon ball so that the children can directly connect the source of the light (the flashlight if you are inside) with the Sun.
Night Sky Network / Astronomy Society of the Pacific has a simple overview of this activity:
https://nightsky.jpl.nasa.gov/docs/MoonPhases1.pdf
and the overview with video support is here: https://nightsky.jpl.nasa.gov/download-view.cfm?Doc_ID=329
https://youtu.be/ai9VcMLBiQg?si=n-RYAcfKFix8jjs4