As Catharina-Amalia, the future queen of the Netherlands, celebrated her fifth birthday this weekend her parents Maxima and Willem-Alexander must have been thinking ahead to another milestone. In January, the little girl, known to her family simply as Amalia, starts school. And in pictures taken during their summer vacation, and recently released to mark her birthday, the cute blonde youngster certainly looked grown up in comparison to siblings Alexia, three, and five-month-old Ariane. The change will mean that from now on vacations, such as those the crown prince and his wife take in the Austrian ski resort of Lech or to visit the girls' maternal grandparents in Argentina, will have to fit in around the school timetable. For now, though, the family, who threw a private party for Amalia's birthday, are focused on the current holidays.