I tried to teach geologic time during a museum summer drop-in program. The age range varied from 4 year old to 5th graders. I tried the calendar way (e.g. the Paleozoic started on November 18th, the Mesozoic began on December 13th, etc.) with visitors using different colors to represent the different eras. Then, to reinforce the concept, we built lego structures depiciting stratigraphy, and tried to correspond the lego block colors to the eras the students had colored on the calendars. It was…mildy successful?
The other activity I tried was creating snap bracelets. We gave visitors stickers and markers to draw the different eras on there. While it was a fun art project, I don’t think many grasped the concept that well. I’d love to re-do it sometime!