The Berlin WelcomeCard (sold by EurAid, BVG offices, the tourist office, and some hotels) entitles one adult and three children under the age of 14 to either two or three days of unlimited travel in the ABC zones for €20.50 or €27.50, respectively, and includes admission and tour discounts detailed in a booklet. A three-day ticket, including admission to all the Museum Island collections, costs €40.50, but it only pays off if you plan on visiting a lot of museums.
Many of the 17 Staatliche Museen zu Berlin (state museums of Berlin) offer several ticket options (children up to 18 are welcomed free of charge). A single ticket ranges from €4 to €8. A three-day pass (Museum Pass Berlin) to 60 museums, including all state museums, costs €24.