Finding out what other people have written about or how big it is or what kinds of people do this interest, is all part of the pursuit and part of becoming a mini expert. Going to the library and learning how to do research has a whole new meaning when you're pursuing your own interest. The same is true for internet searches or finding biographies, autobiographies and fiction that make the interest come alive. It's unlikely that your students will have had previous experience doing Informational Interviews. A little getting ready goes a long way.
Role playing in the class before they step out in the world can make a big difference.
Bring in some other adults to take part in role plays and make it realistic. The students can hold each other accountable, helping you, the teacher, manage the process. They can ask each other good questions to keep the ideas clear. Equally important, there may be additional resources right there in the classroom.