Most parents keep the children together and define that in the even weeks they are with the mother and the odd weeks with the father (or the other way around). Often we see a week - week logic and the week ends on any given day in the week. It happens also that children stay more days with the mother (or the other way around. As long as they stay together any planning is rather easy. The model applied most often you find on the page
May it be that some children are with the mother and others at the same time with the father the complexity increases significantly. Even more when children change more than once during the day.