Swiss Sapphire for Families
Tauck offers family adventures on land, but its river cruise program is really not geared toward family travel; there are no spaces or programs for children onboard Swiss Sapphire or other ships in the line's cruise fleet.
However, don't discount the option if you have more mature children who are hungry for knowledge and don't mind spending much of their time with their parents and other grownups. Bookish teens might do well on a family or multigenerational trip (just remember to point them toward the Wii in the Lido Bar when they get restless).
The youngest "family" on our summer trip was a father and his two kids in their 20's.