Spaceman Spiff. Or something. He got the costume for Christmas from his grandparents, and last night was the first time he put it on. He's been running around shooting us with a toy gun ever since.
Here's a bit of a history lesson, borrowed and paraphrased from Wikipedia (disclaimer: if it's wrong, it's not my fault):
Fastelavn is the name for a Danish carnival held the Sunday or Monday before Ash Wednesday. Although it originated with the Roman Catholic tradition of pre-Lent celebrations, it was later modified into something less religious after Denmark became a Protestant nation. The holiday occurs seven weeks before Easter Sunday and is sometimes described as a Nordic Halloween, with children dressing up in costumes and gathering treats for the Fastelavn feast. (Americans should follow this example. We could use a good mid-February holiday.)
Some towns in Denmark are renowned for their large Fastelavn festivities and parades. Traditional events include slå katten af tønden (hit the cat out of the barrel), which is somewhat similar to using a piñata. The Danes use a wooden barrel, which is full of candy and has the image of a cat on it. Historically there was a real black cat in the barrel, and beating the barrel was superstitiously considered a safeguard against evil. (What a relief they reverted to candy.)
A popular baked good associated with the day is Fastelavnsbolle (Fastelavns bun), a round sweet roll usually covered with icing and sometimes filled with whipped cream. (Must try this.)
Another popular custom is the "fastelavnsris" (often a bundle of twigs decorated with feathers, egg shells, and candy), with which children ritually flog their parents to wake them up on the morning of Fastelavns Sunday. (Their children don't do this every morning? Lucky them.)
Spaceman Spiff, to the rescue! Or, erm, something.