Hier komt kinderkamer 1, kinderkamer 2, kinderkamer 3, kinderkamer 4, kinderkamer 5, kinderkamer 6.

You do not have a link list with a handle set to kinderkamers, or you do and it's empty. Go ahead and create a link list called Kinderkamers on your Navigation page and populate that link list with links that point to collections, to see collections listed here. Make sure the link list also has a handle set to kinderkamers.