I celebrated my second Halloween in Germany last month. Halloween isn't a huge thing here, but people were definitely out celebrating.
I can't say much about what children do here since none of my friends have kids and I was out with friends. On the way to the train station, I some kids and their parents dressed up and standing in the foyer of their apartment. My neighbor's child carved a pumpkin and put it out on the front steps. There are events on the nearby military posts for the military kids, such as trick-or-treating in a centralized area. Beyond that, though, I can't say if the German kids go trick-or-treating, but I think for the most part that they don't.
I saw many adults celebrating Halloween. Our group met up, working on our costumes at our friends' house and enjoying some drinks and snacks. We then went out to stand in line for about half an hour at a club. We decided that was futile so we moved on to a different club to dance. Along the way, we saw many adults in costumes. Most costumes involved face paint and weren't as elaborate as the ones I've seen in the US. I'm also not surprised because there aren't as many options for commercially-available costumes at this time of the year here.
It was a nice night out. I was pleased to meet, in person, a friend of my friend, who had recently visited Detroit. She was looking for company when she was there so I recommended contacting some of my Detroit friends. They hung out over the summer and it was so cool to see Facebook pictures of her with my friends in my old stomping grounds. I then met her in person this weekend so we took a picture and shared it with our Detroit friends. I love how social networks can connect people!