According to the legends, the good old man sends his helpers from the roof tops down the chimneys at night to deliver presents right into the good children's homes. These manoevers explain of course the helpers' faces. There are many other versions.
Suffice it to say that December 6 is a fun day for the kids in Belgium who all wake up earlier than usual, curious to see what the Saint had brought them.
I wish all of them a very happy Sinterklaas/Saint Nicolas!
I have written about the Saint Nic celebrations on December 6 before