During this trip, we had also the chance to visit the neighboring country, Slovakia. The train ride to Bratislava was 1 hour and we decided it was worth it to see another place with the kids. So we took the metro (U-Bahn) to the Vienna central station. There was a train leaving every hour to Bratislava, so we bought the tickets from there and took the next one. The train tickets were quite affordable (12 Euro return for adults and 6 Euro for kids under 15).