Inclusion of children in Dutch passports to be abolished on 26 June 2012
From 26 June 2012 all inclusions of children in Dutch passports will lose their validity. From that day on the child will need to possess its own Dutch passport in order to travel abroad. Therefore, if you want your child to be in possession of a valid Dutch travel document after said date, you are advised to apply for the child's own Dutch passport timely at the Netherlands Embassy in Tokyo. The requirements can be found in Dutch on this page. It takes about 3 weeks for a passport to be issued.
Additional information can be found in this English brochure (pdf).