If it's possible (I don't know the system) what about e.g. underlining all of the kids' stuff, italicizing yours, bolding something else?

Interesting: I too use a Treo, and have a color coded calendar on my laptop & printed output but the colors don't show on my Treo. I use Microsoft Entourage (Mac version of Outlook). Either program supports Categories, which can be color coded & then assigned to each event. Since the Treo can only support about 14 categories, you want to keep these broad. Mine include: Personal (me), DH, DS, School, Holiday, Family, Friends, Travel, Recreation, Vendors (all businesses). The calendar also insists on None & Junk categories. You could also add Work or Office for outside the home employment. Apple's iCal also supports color coded categories.

I don't miss color in my Treo calendar, but I sure would on my laptop. DH saw my color coded calendar & set his up this way too. He prints out his calendar to carry around a month at a glance for meetings & a copy for his office manager.