In Germany the three Thursdays before Christmas are known as Knocking Nights What do children do on those nights?

Answer 1

On a Knocking Night or Klopfelanchten, children wore masks and went from house to house, banging lids and rattling tin cans, and clanging cowbells in their neighbors' front yards. In other areas, costumed groups walk down the streets singing and stop to call at the residents' doors, asking for or giving small presents.

The tradition started because of beliefs that witches and evil spirits committed mischief on those nights during Advent. It sometimes takes a form similar to Halloween in the US.