I have a chip card already ( one with my picture and an anonomous). It says I can add-on a day pass for my 5 year old granddaughter on my card. My question is do I need to checkin twice? The web page is unclear.
Welcome to the world of the Dutch Railways aka NS!
You cannot check in twice. The second check-in will be a check-out. So you need something for the granddaughter.
As far as I can make sense of the information they put on their website, she can have her own OV Chipcard loaded with something called KidsVrij (»KidsFree«). The card comes at EUR 7,50 and the KidsVrij a nominal EUR 0,01. This can be bought online.
Alternatively you can buy her a »Railrunner« ticket, valid for the whole day, at EUR 2,50. Best bought at the window.