Children and young people from 5th to 10th grade travel free of charge in Oldenburg during school hours and use their Mia Junior Card (often combined with the Oldenburg Card to participate free of charge in canteen meals and other discounts). For more information, see question 43!
The bus tickets also can be bought at the service centers of the VWG and at ticket machines in the city center area. You have to show them to the bus driver when entering the bus and in addition single way tickets have to be validated in the validating machine inside the bus. The bus driver can sell you a ticket as well, this ticket doesn't have to be validated afterwards.