We are a family of 3 adults and 3 children (ages 3, 5, 7) in June. We are taking a train from Krakow to Vienna. Should we buy the tickets in advance? We arrive on a Saturday in Krakow and plan to leave Tuesday to Vienna. Would a Saturday purchase be enough time in advance? We are taking the day train. Thanks.
I don't know the answer for that particular route, but what I do to answer this question is to do 2 dummy bookings--one for the your travel date in the future, and one for the same day of the week but in the next week or 2.
The Man in Seat 61 site has a lot of information about this route:
https://www.seat61.com/international-trains/trains-from-Krakow.htm#Krakow_to_Vienna