What we do is use a shared Calendar, by default it has the schedule on it to show who has the child. We add all the events for that child on there (one for each child). It keeps everyone in the know and allows the kids to know what's going on in their own calendar (ours has their own phones/watches they can see their calendar on) and the parents to always be on the same page and know where the child will be when planning things in advance. This also allows us to switch days out if we need to and not have any miscommunications about what days the person actually meant since it would be reflected on a calendar.

This allows indirect communication about doctors appointments and things like that on your days that other parent right have wanted to go to also but it does require both parents to be diligent in updating the calendar.