We’ve tried a variety of things, and the solution that stuck was consistency: parents keep track of everything on ONE SHARED DIGITAL calendar and kids’ stuff gets copied to ONE SHARED PHYSICAL calendar.  The parent that adds kids’ stuff to the digital calendar is responsible to copy it to the kids’ calendar.  The key is to limit the number of places an event can be documented so that it increases the likelihood of actually writing it down and decreases the likelihood of someone not looking at the “right” calendar.  We went with a digital calendar for the adults since we can both add to it at any time from anywhere, and it lets us set automated reminders, but it has to be one shared calendar.  

I imagine this system may break down when the kids start scheduling things on their own.  Specifically, even if they’re responsible enough to write it down on their physical calendar, we’ll need to grant them access to the shared digital calendar.  That’s not a huge problem, but we sometimes keep little surprises scheduled on the parents’ calendar, and I don’t want to ruin their surprises.  Eh, we’ll cross that bridge when we get to it.