Lauren,
it sounds like you have a lot of experience in engaging your infants in the topic and building on their understanding from sources of light to differences between day and night and hence to shadows.
Linking the fact that night is just the Earth’s shadow is a key concept, made clearer by letting children see shadows in their own environment. Perhaps it is the series of rather dull days that we can get in Ireland that make shadow days all the more special (as the Sun has just come out in Cork!).