(Not) UN on Sinterklaas: Yep, we are guilty.

[Kralizec]

To bring you foreigners up to speed, our celebration of Sinterklaas amounts to the following.

A boat arrives at a dock, where a lot of spectators are present - mostly children and their parents. An old guy disembarks. He's wearing a fake beard, red robes and one of those Pope hats. He's accompanied by several "black" guys who pass out candy to children as they pass through the crowd. For some miraculous reason, this event happens at multiple locations throughout the country at exactly the same time.

Later, on the evening of 5 December, children who are young enough to believe in this fantasy leave behind one of their shoes in the living room (near the fireplace, if there is one) and will find a present in (or near) the shoe the next morning, accompanied by a poem signed by "Saint Nick and Black Peter". The parents act as if they're surprised.
That's pretty much it.

As for the mostly white volunteers who usually play the role of Black Peter(s), the dress consists only of black facepaint, a wig of black hair and poofy clothes that were supposedly popular during the Renaissance era. Their role is to interact with the kids joyfully and hand out candy. Acting foolishly is not part of the role - contrary to what the letter to the UN is suggesting, they're not portrayed as submissive retards.
OTOH, Saint Nick is a stern fellow who keeps track of the behaviour of children (writing them down in his "great book") and gives prestents on the night of 5-6 december, but only to the nice kids.

The letter also hints that the character of Black Pete may undermine the Netherlands’ efforts to have the Sinterklaas celebrations recognised as part of official Unesco’s immaterial cultural heritage listings.

On that point, our government said: (paraphrased)

"Contrary to what's being suggested here, we have not filed any request whatsoever to have Sinterklaas added to UNESCO's list of cultural heritage and have no plans to do so."