In the book, The Diary of Anne Frank: The Diary of a Young Girl, why is the Van Daan family invited to go into hiding with the Franks?
The Van Daan family is invited to join the Franks in their secret hideout in the famed story of The Diary of Anne Frank. Mr. Hans Van Daan is a longtime business associate of Otto Frank, and he helped Frank when he and his family first moved from Germany to Holland. So, the magnanimous Mr. Frank asked his friend's family to join them in the safety of the warehouse. The Van Daans did not leave Holland for Switzerland in part because Petronella Van Daan did not want to give up her possessions. Mr. Van Daan was not as receptive to the invitation of Mr. Dussel to stay with them, however, protesting to the Franks that he should not stay.
In addition to the above answer, the Franks went into hiding first because Margot had been called up. The calling up was a prelude to work camps, concentration camps, and possible imprisonment. The Germans increased their call ups from July 13-16, so the van Daams joined them early to avoid the possibility of Peter being called up. As neither family was willing to part with their children and their work/family relationship was present, the families decided to combine forces. The two families were more likely to have the combined resources necessary to survive in hiding.