Where did Frederick William spend part of his childhood during the Thirty Years’ War?

During the Thirty Years’ War, Frederick William was forced to spend part of his childhood away from the Berlin court at the fortress of Küstrin, where he received his education in the Calvinist faith. Additionally, between the ages of 14 and 18, he spent time in Holland, dividing his years between the University of Leiden and the court of Frederick Henry of Orange at The Hague.1