Leah,
the lovely astronomy side to Moonbear’s shadow is the changing direction of the Sun over the course of the day. When I have carried this out with children I have taken them outside first to to see where the Sun is in the sky – we have noted it and it is usually in the south -east (I start my workshops at 10am). We check again when we finish the whole visit (at 1pm) and it is in the south.
When we set up the Moonbear’s shadow fishing pond (a blue bit of paper with some paper fish), I have a compass drawn nearby with the cardinal directions. I ask them — what time of day have you made it? Is the Sun shining from the east – then it is early morning… etc.