When a student is just starting out on the flute, they won't know enough about the repertoire to choose what pieces or exercises to work on. It's up to you to expose them to a representative cross-section of what's out there, but once your students get to an intermediate level, they are perfectly capable of having a role in choosing their music. Developing a sense of ownership in your students is key to their success. Students who feel excited about the music they play will practice more and will be more engaged during lessons.
You should provide guidance and introduce this element of choice in an age-appropriate manner; for less experienced students, being allowed to pick from a list of pieces rather than being assigned a piece to learn is empowering without being overwhelming. For advanced students who know more about the flute repertoire, a simple list of guidelines is fine. Examples of less-specific guidelines are:
The ultimate goal of teaching is to make your students self-sufficient, so encourage your students to make their own decisions whenever it's appropriate. They'll be better musicians for it.