Recently someone asked me how much research is enough to write a book. Do I use 20 sources? Thirty? Do my books for teens require more than the third grade books?
I wouldn’t say that age level plays as big a part in the amount of research that I need to do as the topic itself. If there are books that you can use as resources, I may not have to use as many sources, especially if one or more books has a lot of information. But if the topic is something new with fewer books already on the subject in print? Then I am going to have to use more sources. If you have to use a lot of articles, you will have a huge bibliography.
Perhaps these numberw will show you what I mean. For Ancient Maya, I used 52 sources including a number of books. when I wrote Black Lives Matter, there were no books for teens and almost nothing for adults on this topic. I used 188 different sources. The Zika Virus was similar with so much new material coming out and my bibliography had 120 sources. But what about a book that is something of a survey? Women in Sports covered the history of women in modern sports. Not baseball. Not basketball. Sports. I used 206 sources.
These books are all 15,000 words long. My books for 3rd graders are much shorter at 3500 words. 12 Incredible Facts about the Cuban Missile Crisis required 43 sources and I used 48 for the book on esports, both of which are comparable to the number of sources I used for the Maya book.
Although I understand why I teacher would tell a student to use 5 sources or 10, I would never answer this question with a number. There is just too much variety depending on the topic and what else is in print. Instead, I would say that you should research until you can start writing.
Just start. Develop an outline if you are writing a longer book. If you are writing a picture book, outline it and maybe rough it out. This will tell you where you information is scant and what you still need to research. I don’t worry about researching too much. Research is too much fun to get stingy about it. But I also don’t worry about researching too little. If you’ve come up with a topic that has never been covered, which is what you need to do to sell, you are going to have to put in the work required to write a full and satisfying manuscript. That is what is necessary much more than a specific number of sources.