The Metopolitain Museum of Art has a set of Egyptian Hieroglyph rubber
stamps (with key) that would be fun to use to press the designs in clay or
to print on "papyrus". They can use the key to spell out messages, etc.,
though they'd have to share. I think they run from $11 to $15 for a set
(sometimes they're on sale).
After they're familiar with hieroglyphs, are they going to design their own
syllabary or alphabet of shapes?