Moving in Vienna with children

Hi! We are a family of four and we are moving in Vienna on summer. Our children are 9 and 13 years old. They don't speak German. They are both great pupils with highest marks. What can we  expect for them when they will start going to school in Vienna? We would like them to go in public schools and to become fluent in German? Is it possible for our older son to go in Gymnasium after two years in Mittelschule? Thnx in advance

Children adapt very quickly when learning a new language so I would not worry too much and they will get extra help.

@SimCityAT  thank you for your answer. We are less worried about our younger son. But we have some worries about older son and his path through education in Vienna

I also have a bilingual 13yr old in Vienna.  Feel free to contact me and you could call me if you like.