Family as a relationship of cooperation and solidarity refers to responsibility and education between generations. Often, the intermingling of mutual responsibility of all family members and upbringing within a specific parent-child relationship is not at all obvious. But it is set in motion when a child falls ill with leukaemia and the sibling becomes a donor, because care of the sick child changes the family structure, and thus what parents understand by responsible action and the significance that education has. In the first section, I deal with education, responsible parenthood and family issues. The second part discusses family and illness. This is followed by an analysis of the Kirstein family from the Lübeck project on bone marrow donation between siblings, in which a child has been diagnosed with leukaemia. Finally, I work through the different dimensions of responsibility in education and family interaction in the family structure.