Today many Dutch families are celebrating St. Nicholas evening (Sinterklaasavond in Dutch). This includes Bjørn and his family. The tradition starts a few weeks earlier, where they draw names blindly to determine who's going to take care of which present. The objective, then, is to create a surprise around the present and write a poem to go with it, all in secret. In a few hours the mythical St. Nicholas will pass their home and somebody will be knocking the door very loudly. This is where they come out to find the surprises they made, as if St. Nicholas left them there. Nobody actually believes this anymore of course, but they all believed St. Nicholas existed when they were young.
This shows partly that you can make children believe almost anything, even that some old man keeps visiting the Netherlands from Spain, later leaving presents on everybody's doorstep on the same evening and go back to Spain. When St. Nicholas actually knocks the door and enters the house, to the children that's him and of course he exists because they can see him right there. This early in life, there is not much to relate this to, and you have hardly any idea about scale, distance or time. Good thing we all eventually come to our senses, though some people come to their senses more than others.