The Woebegone twins

Twins Greta and Feliks are rescued from the Schwartzgarten Reformatory for Maladjusted Children by Olga Van Veenen, a fabulously wealthy children's author, plagued by writer's block. When Olga disappears, Greta and Feliks a competitor is to blame but are able to rescue their guardian. As if by magic, Olga's writer's block lifts, and she quickly produces a new book, that has eerie similarities to the twins' adventures in Castle Van Veenen, and Greta and Feliks wonder whether Olga deliberately used them for literary inspiration.