Visiting Berlin

Hello, I will be visiting Berlin for 3 days with my 4 children ages 7-13 in April. We are very excited, but I have a few questions.

1. I've heard that the trains have been less than reliable, but I don't know what that means. We will be traveling from Poland (though we are American). Should we expect trains to be about an hour or so late, or do they just not come at all? We aren't going to be in a rush, but I don't want to be stranded!

2. I learned German well 20 years ago, and I still read and understand it well, but my speaking skills are rusty from disuse. How patient are people likely to be as I attempt to speak German?

3. Do you have any advice for a mother travelling with her children? I went to Germany many years ago, but never to Berlin. I've found sites and museums we are looking forward to visiting, but recommendations from those who actually know are very welcome!