Just choose some catchy children's songs, and try not to choose pop songs, such as "Where is Spring" and "Edelweiss". The whole tune has a narrow range, and the tune is familiar, cheerful and pleasant, and easy to express. Choose a tune that suits your range, I think it will be very effective. In addition, you can prepare the rhythm of the dance, mainly the coordinated rhythm of the limbs.
Generally speaking, the interview will include two aspects: trying to speak and answering questions. If you try to speak, you will usually be told what course you want to try to speak at least one day in advance, so that you can prepare in advance. Some schools will also let you answer questions on the spot during the interview, which may be professional or the work of the class teacher.